He's not anti war as much as he's anti policy that pushes up against Russian spheres of influence. You see no issue with, and in fact a lot of funding and support increase to, Saudi Arabia. Where as Obama had put a pause on things during the initial outbreak. Didn't condemn things outright in public, but the Obama administration was definitely taking a step back during the Yemen war.

The trump administration also has changed the rules of engagement for military strikes on ISIS and other terrorists to allow for the potential of more collateral damage or civilian deaths. The Obama administration set that threshold pretty high to prevent blowback for our actions and feeding terrorist propaganda.