The “Phoney War” was an eight‑month build-up to war

Germany’s invasion of Poland in 1939 launched World War II

On September 1, 1939, Nazi Germany launched a surprise invasion of Poland using blitzkrieg—coordinated air bombardments and armored assaults—to overwhelm Polish defenses within weeks. This lightning-strike strategy shocked the world and signaled both the start of World War II and a revolutionary shift in modern military tactics.

European leaders pursued appeasement of Hitler in the 1930s, hoping to avoid war.

Hitler declared war on the United States four days after Pearl Harbor

Despite having no treaty obligation to join Japan’s fight, Hitler declared war on the US on Dec. 11, 1941. The move pulled America into the European theater and is widely seen as one of Hitler’s most strategic blunders.

The Nazis and Soviets agreed to a non‑aggression pact in 1939

On August 23, 1939, Nazi Germany and the Soviet Union signed the Molotov–Ribbentrop Pact—a public commitment to not attack each other combined with a secret agreement dividing Eastern Europe into spheres of influence. This pact enabled Germany to invade Poland unopposed from the east and delayed conflict with the USSR until June 1941.

Before Pearl Harbor, the US was a nonbelligerent ally to the Allied powers

Between September 1940 and December 7, 1941, the United States remained officially neutral—yet President Roosevelt incrementally shifted policy from “cash‑and‑carry” to Lend‑Lease, funneling critical military aid to Britain and other allies without entering the war.

Since World War II, formal declarations of war and peace treaties have become increasingly rare, replaced by cease-fires, authorizations of force, and "special military operations."

Congress has formally declared war 11 times across five conflicts, the last in 1942

The five declared wars were the War of 1812, the Mexican-American War, the Spanish-American War, World War I, and World War II. Every major American military conflict since Korea, Vietnam, Iraq, and Afghanistan has been fought without a formal declaration.

Germany’s surprise offensive in December 1944 failed to break Allied lines

In a bold counterattack from December 16, 1944, to January 28, 1945, Hitler committed over 400,000 troops in a surprise “Bulge” through the Ardennes forest in France. Although initially successful in creating a 50‑mile incursion, Allied defense halted the advance. German forces suffered irrecoverable losses (~100,000), while Allied casualties totaled ~75,000, marking the offensive as the last major German gamble and a decisive step toward Nazi defeat.

'Keep Calm and Carry On' was long-forgotten World War II propaganda

The British Ministry of Information developed the stoic phrase ahead of German attacks at the start of World War II in 1939. It was never officially released on posters and then lay dormant until 2000, when one of the remaining posters was discovered at a bookstore in the UK. It has since been adapted into countless memes.

The treaty that ended the First World War laid the groundwork for the Second.

A 1983 NATO war simulation provoked the Soviets to prepare for war

The "SNAFU" podcast, hosted by actor and comedian Ed Helms, explores some of the biggest blunders in history. Season one focuses on the 1983 NATO Able Archer military exercise, a war game that simulated nuclear attacks on the Soviet Union. The USSR mistook the exercise for a genuine threat and prepared its forces for war. Helms recounts this almost catastrophic event in world history with his signature humor.

Governments have historically used counterfeiting for economic warfare

Inserting fake currency into an economy can help destabilize it. During the American Revolution, for instance, the British distributed counterfeit “Continental Dollars” in an effort to devalue the currency being used in the US at the time with the goal of undermining America’s growing financial credibility. The Nazis also ran an extensive counterfeiting scheme during WWII.

Japan's imperial expansion in Asia in the 1930s set the stage for war with the US.

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World War II helped convince food companies to produce more processed foods

Processed foods had existed since the 19th century, but they began infiltrating the mainstream during World War II, with foods designed to last on the battlefield for days. After the war, food companies saw great potential in the relatively cheap foods aimed at busy households. (Some readers may experience a paywall.)

World War I causes

World War I was, as the name says, truly war on the global scale. Fought between the French, Russian, British, Austria-Hungary, Ottoman, and Russian Empires, it was in part, a battle for territory. And after the war ended, several of these empires collapsed. Explore the different causes of World War II in this article.

D-Day, history's largest amphibious invasion, turned the war's tide

On D‑Day, over 156,000 American, British, and Canadian troops assaulted five heavily defended beaches along a 50‑mile stretch of northern France. Supported by nearly 3 million men, 1,200 warships, and 13,000 aircraft, the successful landings paved the way for the liberation of Western Europe and decisively shifted momentum against Nazi Germany.

Illustrating the beginning and end of WWI through maps

In August of 1914, Germany invaded an ostensibly neutral Belgium, kick-starting World War I. The war became one of the deadliest conflicts in human history, decimating Europe and reshaping global politics for the next century. It also brought forward sweeping and terrifying new military technologies, a product of the Industrial Revolution. Explore 40 maps explaining the Great War in detail.

Wartime conferences exposed cracks in the US–Soviet alliance

At the Tehran, Yalta and Potsdam Conferences, Allied leaders coordinated WWII strategy—but deep disagreements over postwar Europe foreshadowed the Cold War. The USSR’s push for influence in Eastern Europe clashed with US and British calls for self-determination.

The 1956 Suez crisis was one of the earliest tests of the rules-based order

When Britain, France, and Israel secretly invaded Egypt, the Eisenhower administration supported UN resolutions condemning the invasion and called for a ceasefire—publicly criticizing its closest allies to uphold the principle that force should not be used to resolve international disputes.

The first test of America's war powers came just a decade after the Constitution was ratified

During the undeclared Quasi-War with France in 1800, the Supreme Court ruled in Bas v. Tingy that Congress had authorized a valid "imperfect war" through statutes alone, without a formal declaration, establishing that there is a legal spectrum between peace and declared war.

See what it was like to live in the United States during World War II

In America, life was transformed by total war: sixteen million service members left civilian life, while massive industrial production demanded labor. Women, minorities, and teens filled factories, fueling boomtown growth and breaking social barriers. Simultaneously, rationing, recycling drives, Victory Gardens, ration stamps, blackout drills, and war bond campaigns permeated daily routines.

British Prime Minister Churchill’s speeches rallied the nation

Winston Churchill’s impassioned wartime oratory united Britain’s resolve, transforming fear into defiance and forging a path to continued resistance against Nazi aggression.

Why did the US make it illegal to sell sliced bread during WWII?

Pre-sliced bread has only been with us for almost 100 years, but during the course of World War II it was briefly banned to save on supplies like wax paper and stainless steel for the war effort. This Atlas Obscura article explores this amusing (though not at the time) bit of food during wartime history.

The attack at Pearl Harbor required nearly a year of planning and preparation

In early 1941, Admiral Isoroku Yamamoto ordered detailed planning for a surprise carrier strike on Pearl Harbor. Japanese teams spent months refining torpedo modifications, training pilots, and rehearsing the complex attack.

Franklin D. Roosevelt's 1941 speech framed World War II as a global fight for universal rights

Eleven months before the attack on Pearl Harbor, President Roosevelt outlined four fundamental freedoms that, in his words, people "everywhere in the world" ought to enjoy—speech, worship, freedom from want, and freedom from fear.

In 1914, the Financial Times asked readers to redraw Europe for cash prizes

Two months in World War I, the newspaper invited readers to sketch postwar borders and submit peace terms for cash prizes. The contest captured public attempts to predict a new world order and foreshadowed modern crowdsourced forecasting. It's a wild look at how uncertain Europe's future was at the time.

In 1938, 1.7 million people were fooled into believing a Martian invasion was underway because of a radio play

Orson Welles' realistic radio dramatization of a Martian invasion of Earth, called "The War of the Worlds," caused quite a stir with audiences. The broadcast resulted in panic, with some people in the area where the story took place attempting to flee. It also helped Welles secure a contract with a Hollywood studio, leading to the creation of "Citizen Kane."

The Japanese Navy used radio silence and deception to mask its approach

In late November 1941, Japan’s carrier strike force maintained total radio silence while operators back home broadcast normal traffic—creating ambiguity about the location of the fleet. The deception obscured US intelligence and helped create a surprise attack.

Should the US have entered into World War I?

America entered World War I in 1917, but had remained neutral until that point. President Woodrow Wilson addressed Congress, further underlining the USA's neutrality. Eleven weeks later, he asked for a declaration of war. With attacks by German saboteurs on an American munitions depot, it seemed he had no choice. But did he? This article asks what might have happened if the US stayed out of WWI.

Before World War II, the US was a Pacific power

Decades before Pearl Harbor, the US held major Pacific territories—Hawaii, the Philippines, Guam, American Samoa, and numerous island bases—giving it strategic reach across the western Pacific. This presence increasingly overlapped with Japan’s imperial ambitions in the region, contributing to rising tensions.

Disney chipped away at its debt by creating propaganda during World War II

Disney began producing training videos for the Navy and propaganda films for US involvement in World War II, including the shorts "Der Fuehrer's Face," "The Spirit of '43," and "Donald Gets Drafted." The effort provided a much-needed cash injection, allowing Disney to continue producing films.

Champagne played a role in resisting the Nazis

When France surrendered to the Nazis in 1940, the invaders occupied the north. This was home to wine regions like Champagne and Bordeaux, which the Nazis were eager to loot. Winemakers took a stand by sheltering dissidents in their cellars, passing intelligence across borders, and even giving their lives to the cause.

Detailing the horrific conditions of life in the trenches

What was it like to live and fight in a trench during World War I? If you were on the German side you might have bunkers, electricity, and other basic comforts. If you were on the British and French side the conditions have been described as muddy and "horrific". Find out how unpleasant trench warfare was and how it affected WWI soldiers.

How much did WWII cost?

Though it lasted fewer than four years, World War II was the most expensive war in United States history, according to this infographic. Read through it to see how much WWII cost and learn about the consequences of financing such an expensive conflict.

In the 1980s, excerpts from fake diaries of Adolf Hitler were published in a prominent German magazine

Excerpts from the diaries were published in other publications around the world, like The Sunday Times, despite uncertainty about their authenticity. After forensic analysis, the diaries were proven to be fake. The diaries were produced by Konrad Kujau, a petty criminal who frequently produced counterfeits.

Can you save Britain from the Nazis by carefully sharing secrets with America?

Find out in this 20-minute interactive graphic novel based on true events from World War II.

The Cold War (1947-1991) prompted the birth of NATO and the Soviet Warsaw Pact

The geopolitical rivalry between the United States and Soviet Union was considered “cold" because the two countries never directly engaged in military combat during the time period. This page from the Kennedy Presidential Library outlines the causes and major events of the early Cold War.

In the 1930s, Congress nearly passed a constitutional amendment requiring a national vote before declaring war

The Ludlow Amendment, proposed amid rising isolationism after World War I, would have required a national referendum before Congress could declare war, except in cases of direct attack. It was defeated 209 to 188 in 1938 after Roosevelt lobbied against it.

Radar saved the British Royal Air Force from Nazi air assaults

Radar technology—particularly the Chain Home early-warning system—enabled the RAF to detect incoming Luftwaffe raids up to 80 miles out, coordinate fighter deployments through the Dowding System, and achieve interception rates over 90%. This technological edge was pivotal in winning the Battle of Britain and halting Germany's air campaign.

Explaining the final battle of World War I

The Meuse-Argonne Offensive was the last battle of the First World War. Beginning in September and ending November 11, 1918, the battle was a tumultuous event and the first time the American Army fought on the world's stage. America simultaneously achieved victory and discovered new methods to fight a war. This Apple History podcast provides the details.

How the US entered WWI in 1917

Originally taking a position of neutrality during the course of World War I, the United States of America eventually relented. Entering the war in 1917, support for the British and French had risen and Americans were incensed by Germany's overtures to Mexico and U-boat attacks that sank ships and ended American lives. See how and why the US entered WWI in this article.

Orson Welles' 1938 broadcast of 'War of the Worlds' invoked real panic

The raconteur's teleplay of HG Wells' 1898 science fiction novel presented the plot as a news broadcast, leading some listeners to believe that New Jersey was being invaded by Martians. This retrospective from the National Endowment for the Humanities unpacks how he made it happen, and the media fallout that ensued.

When German submarines lurked in US coastal waters

During World War II, German submarines (also known as U-boats) prowled the Southern coast of the US in 1942 and 1943, sinking more than 60 ships and killing 600 Allied soldiers. The campaign is less well-known, since the major battles in Stalingrad and Midway happened at the time. Several of these submarines and the ships they sank are now popular diving spots.

A formal declaration of war automatically triggers hundreds of statutes granting the president sweeping domestic authority

Beyond authorizing military force abroad, a formal declaration activates a wide range of domestic powers, including authority over enemy property, trade restrictions, and emergency economic authority. It also waives the 60-day time limits under the War Powers Resolution.

Was WWI really the first world war?

Was World War I the first true international conflict? This article thoroughly explores the meaning of the term world war. It also suggests a few previous conflicts, some of which involved battles in the Americas as well as Europe, that might have been more accurately described as a "world wars."

Penicillin production was just behind the atom bomb in wartime priorities

By 1943, the US War Department made penicillin its second-highest priority—just after the Manhattan Project. Producing enough of the antibiotic for the D-Day invasion became a central mission of Allied science and industry.

The 1915 sinking of the Lusitania precipitated World War I

In 1915, the British RMS Lusitania sank after being torpedoed by a German submarine. The Germans claimed the ocean liner was transporting munitions. Almost 1,200 civilians were killed in the disaster, which became a symbol of German aggression in the lead-up to World War I.

An interactive timeline of the major events of World War I

World War I took place between July 28, 1914 and November 11, 1918, but a lot happened within that relatively short time. And even more occurred afterward. The comprehensive timeline shows when major and influential events took place during the conflict, accompanied by articles, videos, and other media in support.

Comic books were a major part of American propaganda efforts during WWII

See how US comic books, alongside international counterparts, served as powerful wartime propaganda tools from 1941 to 1945—boosting morale, promoting war bonds, and demonizing Axis powers through the use of iconic heroes and patriotic messaging.

The 1967 war was the first use of oil as a geopolitical weapon

Following the June 1967 Arab–Israeli war, Saudi Arabia, Kuwait, Iraq, Libya, and Algeria embargoed oil shipments to the US, UK, and West Germany. While the move did not have a large impact, it reshaped global oil flows, and foreshadowed OAPEC's later actions.