While researching a history paper, you see a graph that shows federal spending on defense in the past 200 years. You notice that federal spending throughout the late 1900s shows much more spending on defense than in previous decades. What development most likely caused this sustained increase in US peacetime defense spending?

This is in fact not true, federal spending on defense in the late 1900s specifically the 1990s was in a decline from previous years when spending on the Cold War was very high. However, in the early 2000s defense spending increased dramatically with the introduction of the War on Terror and also the wars in Iraq and Afghanistan.