You might make a compelling argument that us defense spending hasn't helped conflict abroad, but the last military conflict of note on us soil was Pearl Harbor in World War II.
A reasonable person might conclude that us defense spending has been very effective at preventing military conflicts on us soil.
And maybe the case that us defense spending even increases the number of global conflicts if it reduces the chance of conflict at home.
The question isn't if the US defense spending increases or decreases total conflict, but for whom it increases or decreases conflict