Significant U.S. Conflicts

The United States wins the Spanish-American War and acquires foreign territories—Puerto Rico, Guam, and The Philippines.

World War I begins.

The U.S. abandons neutrality to join the Allies in world War I.

World War I ends.

The Senate rejects the Treaty of Versailles and American membership in the League of Nations.

The U.S. declares the war with Germany to be at and end.

Germany invades Poland and World War II begins.

Japanese forces assail Pearl Harbor. The U.S. declares war on the Axis Powers and enters World War II.

End of World War II. The U.S. is a founding member of the United Nations.

The end of World War II marks the beginning of the Cold War. Fearing the spread of Communism in war-torn Western Europe, the United States inaugurates the Marshall Plan.

The U.S. and 11 other nations sign the North Atlantic Treaty, forming NATO.

Communist North Korea invades South Korea. President Truman sends American troops to defend South Korea. The U.S. goes on to lead forces from 15 other nations in the Korean War (1950–1953).

The U.S. Senate passes the Gulf of Tonkin Resolution at the request of President Johnson. The Resolution approves U.S. military involvement in the Vietnam conflict.

President Nixon orders a halt to offensive operations in North Vietnam on Jan. 15 and representatives from all sides sign a peace pact, ending the longest war in U.S. history. The last American troops depart by March 1973.

President Reagan orders an invasion of Grenada to establish order on the island and eliminate the Cuban military presence there. A U.S. peace-keeping force remains until 1985.

The Berlin Wall comes down, marking the end of the Cold War.

President Bush sends troops to Panama to depose and capture Manuel Noriega, who had been indicted for drug trafficking.

Persian Gulf War—the U.S. leads a coalition of 32 countries to drive Iraq out of Kuwait, which it had invaded.

U.S., Canada, and Mexico ratify the NAFTA free-trade agreement.

A U.S.-led multinational force attempts to restore order to war-torn Somalia so that food can be delivered and distributed within the famine-stricken country.

After Haiti's democratically elected president Jean-Bertrand Aristide is ousted in a coup in 1991, a U.S. invasion three years later restores him to power.

During the Bosnian civil war, which begins shortly after the country declares independence in 1992, the U.S. launches air strikes on Bosnia to prevent ethnic cleansing. It becomes a part of NATO's peacekeeping force in the region.

The U.S. is a founding member of the World Trade Organization (WTO), formed to monitor and promote world trade.

Yugoslavia's province of Kosovo erupts in war in the spring of 1999. A U.S.-led NATO force intervenes with air strikes after Slobodan Milosevic's Serbian forces uproot the population and embark on a plan of ethnic cleansing of Kosovo's ethnic Albanian population.

After the September 11, 2001, terrorist attacks, the U.S. declares war on terrorism.

Operation Enduring Freedom—the U.S. invades Afghanistan and deposes the Taliban, who had sheltered terrorist leader Osama bin Laden.

The U.S. launches Operation Iraqi Freedom, an invasion of Iraq, as part of the war on terrorism.

On Aug. 31, President Obama announces the end of U.S. combat missions in Iraq.

Operation New Dawn begins on Sep. 1. A U.S. transitional troop force will remain in Iraq, tasked with the mission: "advising and assisting Iraq's Security Forces, supporting Iraqi troops in targeted counterterrorism missions, and protecting our civilians."

On May 2, 2011 (May 1 in the U.S.), U.S. troops and CIA operatives shot and killed Osama bin Laden in Abbottabad, Pakistan.

May 1, 2012, President Obama and President Karzai signed the Enduring Strategic Partnership Agreement between the Islamic Republic of Afghanistan and the United States of America. The Agreement provides for the possibility of U.S. forces in Afghanistan after 2014, for the purposes of training Afghan Forces and targeting the remnants of al-Qaeda. Afghanistan will be a “Major Non-NATO Ally” and as such, the U.S. will support the training, equipping, advising and sustaining of Afghan National Security Forces, and social and economic assistance.

Reacting to instability due to Syria's civil war, the U.S. sends troops to neighboring Jordan--to contain the border; and Turkey--to prevent any Syrian-based missile strikes.

According to the Department of Defense, 6,097 targets were damaged or destroyed as of April 23, 2015. The strikes were conducted as part of Operation Inherent Resolve, an undertaking meant to eliminate the Islamic State of Irag and the Levant (ISIL) terrorist group and the threat they pose to Iraq, Syria, the region, and the wider international community. Coalition nations conducting airstrikes in Iraq include the United States, Australia, Belgium, Canada, Denmark, France, Jordan, the Netherlands and the United Kingdom; coalition nations conducting airstrikes in Syria include the United States, Bahrain, Canada, Jordan, Saudi Arabia and the United Arab Emirates.