Europe

1941–1945 · $4.8T · 405,399 US deaths

The deadliest war in human history. US entered after Pearl Harbor. Fought on two fronts across three continents.

1917–1918 · $380B · 116,516 US deaths

US entered the "war to end all wars" after German unrestricted submarine warfare and the Zimmermann Telegram. 2 million Americans deployed to Europe.

2022–Present · $175B · Covert

Following Russia's full-scale invasion of Ukraine on February 24, 2022, the United States has provided over $175 billion in total assistance — approximately $66.9 billion in military aid, $26 billion in financial/economic support, and $80+ billion in additional security and humanitarian assistance. This represents the largest U.S. military aid package since World War II's Lend-Lease program. Weapons deliveries have progressively escalated from Javelins and Stingers to HIMARS, Patriot air defense systems, Abrams tanks, Bradley fighting vehicles, ATACMS long-range missiles, cluster munitions, and F-16 fighter jet training. The aid has been accompanied by extensive intelligence sharing, satellite imagery, electronic warfare support, and training programs for Ukrainian forces at bases in Germany, the UK, and other NATO countries. No U.S. troops have been deployed in combat roles, but the scale of support makes the U.S. a de facto co-belligerent in the largest land war in Europe since 1945.

1995–2004 · $35B · 12 US deaths

The Bosnian War intervention (1995-2004) marked the first time in NATO's 46-year history that the alliance used military force — not to defend a member state from attack, but to halt a genocide unfolding in the heart of Europe. After three years of Western paralysis during which an estimated 100,000 people were killed, 2.2 million displaced, and systematic ethnic cleansing including the Srebrenica massacre of 8,000 Muslim men and boys occurred under the watch of UN peacekeepers, NATO finally launched Operation Deliberate Force in August-September 1995, a sustained air campaign against Bosnian Serb military positions. Combined with a Croatian-Bosniak ground offensive, the bombing brought Bosnian Serb leaders to the negotiating table, producing the Dayton Accords in November 1995. The United States deployed 20,000 troops as part of the 60,000-strong Implementation Force (IFOR), later succeeded by the Stabilization Force (SFOR), maintaining a peacekeeping presence through 2004. The intervention cost approximately 8 billion (5 billion inflation-adjusted) and resulted in 12 American deaths — none in combat — making it one of the most effective military interventions in modern history in terms of lives saved. However, it came years too late, after genocide had already been committed, and created a dysfunctional Bosnian state that remains ethnically divided and essentially ungovernable three decades later.

1998–1999 · $10B · 2 US deaths

The Kosovo War (1998-1999) was a defining moment in post-Cold War international relations: NATO's first offensive military operation, conducted without United Nations Security Council authorization, without U.S. congressional approval, and against a sovereign nation that had not attacked any NATO member. For 78 days from March 24 to June 10, 1999, NATO aircraft flew over 38,000 sorties and dropped more than 23,000 bombs and missiles on Yugoslav military targets and infrastructure in an effort to halt Serbian President Slobodan Milošević's campaign of ethnic cleansing against Kosovo's Albanian majority. The campaign, Operation Allied Force, was conducted entirely from the air — with aircraft flying above 15,000 feet to minimize pilot risk — resulting in zero U.S. combat deaths but an estimated 500 civilian casualties from errant bombs, including the accidental strike on the Chinese embassy in Belgrade that killed three journalists. The bombing ultimately succeeded: Serbian forces withdrew from Kosovo, a NATO peacekeeping force (KFOR) of 50,000 troops occupied the province, and Kosovo eventually declared independence in 2008. But the precedents set — humanitarian intervention without UN authorization, executive war-making without congressional approval, and "risk-free" warfare conducted entirely from altitude — fundamentally reshaped international law, NATO's identity, and the American approach to military force.