There is a lot that you could consider for a paper focusing on changes in American warfare. Most military conflicts that the United States has been involved in during recent decades can be described as fourth-generation warfare (4gw). This refers to decentralized combative situations in which the lines between civilians and combatants are often blurred. In terms of the war on terror, this is almost always the situation, since the United States has frequently been engaging with non-state actors. Indeed, with the exceptions of the Gulf War of 1990–91 and the initial invasion of Iraq in 2003, the United States military has not engaged on any large level with another conventional military since the end of the Vietnam War.
This type of warfare has its modern origins in the Cold War, where superpowers, including the United States, found themselves engaging with postcolonial forces and populations, often employing unconventional tactics. Unlike state-versus-state conflicts, there are seldom clear battlefronts and enemy forces can blend into and utilize the resources of local populations. This was the case in Somalia, post-invasion Iraq, Afghanistan, and several other more recent military conflicts.
These changes have significantly changed the nature of the United States military. For your paper, you could focus on how US military engagement now incorporates a significant amount of cultural engagement and goodwill elements in addition to more traditional martial responses. This is now a necessary part of warfare. With the enemy often relying on local support, American forces need to understand and win the trust of the local populations. This shows how the goal of military intervention has shifted from being purely combative—inflict physical harm on the enemy—to winning over support from the population in the combat zone. In this way, the military has become more of an extension of diplomacy rather than an alternative to it. Granted, the US military still works hard to destroy the enemy's ability to fight, but this newer element has become just as important.