In 1917, Germany re-started its submarine attacks against unarmed ships even though it had pledged to stop. U.S. President Woodrow Wilson asked the U.S. Congress for a declaration of war, and the U.S. entered World War I.

In 1940, Germany, Italy, and Japan signed an agreement forming an alliance. They hoped to keep the U.S. out of World War II. President Franklin Roosevelt asked Congress for aid to help Great Britain fight these powers.

On December 7, 1941, Japan attacked Pearl Harbor, Hawaii. The next day, U.S. President Franklin Roosevelt asked the U.S. Congress for a declaration of war against Japan. Congress acted quickly, and the U.S. officially entered World War II.

In order to defeat Germany in World War II, President Franklin Roosevelt worked with Great Britain to plan a major invasion of western Europe. In 1943, he appointed General Dwight Eisenhower to lead the attack.

In 1949, after World War II, the United States and other democratic western countries formed NATO, the North Atlantic Treaty Organization. It said that if any country was attacked by an outside nation, they would help defend each other.

After World War II, the United States gave more than $13 billion to help rebuild countries and support their democratic governments.

During the Cold War, the United States was determined to stop communism from spreading. When communist North Korea invaded South Korea in 1950, President Truman sent U.S. troops to help stop the North Koreans.

In 1968, the major countries of the world agreed to the “Nuclear Non-Proliferation Treaty” in order to limit the spread of nuclear weapons.

In 1990, Iraqi leader Sadam Hussein invaded and took over neighboring Kuwait. In January 1991, Congress authorized President George H. W. Bush to lead U.S. troops into Kuwait and force the Iraqi troops to leave.

In 1993, the United States, Canada, and Mexico agreed to the North American Free Trade Agreement (called “NAFTA”), in order to make trade easier among the three countries.

On September 11, 2001, al-Qaeda terrorists attacked the United States. President George W. Bush asked Congress for authority to use military force against those responsible. U.S. troops were sent to Afghanistan, where al-Qaeda leaders were based.

In January 2010, a terrible earthquake devastated Haiti. The United States sent food, water, and medical care to help those affected.

In 2013, the U.S. Agency for International Development’s “Water Supply, Sanitation & Hygiene” program in West Africa helped over 28,000 people get access to a better source for drinking water.

The United States ws the first country to approve of the document that created the United Nations, after WWII, that tries to keep world peace.