It's interesting. In 2008 and 2012, Ron Paul held the philosophical position of not getting involved in foreign conflicts (i.e. the founding fathers didn't want the U.S. to get involved in entangling alliances), leading some Republicans at the time to incorrectly label him as isolationist. Due to his perceived lack of support even for Israel, most Republicans didn't really care for him.
I think people generally want to save the world, but they don't want to get emotionally invested or for a war to escalate, resulting in sending in their kids and grandkids, as is often the case. They also don't want to increase the national debt faster in order to fund a potentially long, drawn-out war.
Taking a utilitarian approach, in such situations as a world power attacking a much smaller country over a territorial dispute (am thinking of the situation in Ukraine), perhaps initially helping the smaller country defend itself against the much more powerful country would make sense. It would give the smaller country time to mobilize its military, while also providing time for many who may want to leave the country to do so, with the goal of restoring peace as quickly and efficently as possible. On the other hand, a protracted war could cause conflict to generally escalate in the region and increase the risk of use of nuclear weapons. It would seem the best strategy may be initial financial and military aid (without sending in actual troops to fight), followed by either aggressive peace talks or committing to staying in the war for as long as it takes in order to defend the smaller country, which could be decades or longer, perhaps causing greater harm to all involved than if the former strategy was used.
Hopefully in the future, things move towards finding ways to quickly and peacefully resolve conflict.