Here's my proposal, specific to the USA for reasons which will be apparent:
Any the government wishes to engage in compbat action, that tax year each citizen is taxed the full cost of that deployment. Including combat salaries, VA benefits, hardware, fuel, everything.
So if the government wishes to spend a puny $20 billion dropping 'smart' bombs on whoever, that's $100 extra tax on each person, not subject to any loopholes, no income restrictions, no getting out of it. Everyone pays upfront, no passing the cost to grand kids.
The Iraq War (#2) would have cost each person $10,000-ish. My guess is that after the first $1000 tax bills came in, that war would have wound down quick. Or better, when the cost estimates of starting the war in the first place came out, no one would support it given the flimsy reasoning.
I do think people would support limited military action. Going after al Qaeda after 911....people would come together and pay for that. Sticking our nose in Syria's...less likely.
Side benefit is it would make Pentagon more dollar conscious as well.
People react strongly to 'pricing'.