I lifted this out of Tom Clancy's Executive Orders.
Those of you familiar with the story may recall that, at the end of the novel, 
President Ryan orders the execution of the Iranian head-of-state for waging war 
on the US, and promises to do the same to anyone else who tries to do so again.
Since reading it, I've been thinking: What if this protection was extended to 
other nations? What if the United States promises to execute any national 
leader who declares war on a nation protected by the US?
At the least, I think that it would make despots hesitate to invade their 
neighbours if they knew that they personally would die for doing so. The best 
result would be that there would be no more war, because everyone who can 
declare it is too scared to do so.
To be even more effective, the protection can be modified so that if the 
protected nation wages war, the protector is oblidged to execute their leader 
also. Then the protection is provided at the descretion of the protector 
nation, and can be withdrawn at any moment. I foresee that weaker nations will 
seek protection from several strong nations, nations that CAN carry out the 
threat of executing an aggressor's leader. Also, the provision of this 
protection will be at the core of diplomatic negotiations.
Think about it, don't like the way their goverment is running the country? 
Withdraw protection and they will have to start worrying about their hostile 
neighbours...
It doesn't kill the greed that makes leaders wage war, but at least it ensures 
their punishment for the crime. It also can't stop things like local 
insurrection or civil war, other than that I think it's perfect.
But I'm sure there has to be a loophole in my thinking. A loophole which a mean 
leader thinks he can use to conquer another nation while escaping the wrath of 
its protector. That's where the story is, and that's where I could use ideas 
from you.
So got any?