Two studies that have found some evidence that the timing of death responds to incentives created by changes in estate taxes:
1. From the USA: Kopczuk and Slemrod (2003), https://pdfs.semanticscholar.org/afd2/7f878ba71c9ec28258407a1e9b34150cd9d0.pdf
2. From Sweden: Eliason and Ohlsson (2013), http://www.diva-portal.org/smash/get/diva2%3A457378/FULLTEXT01.pdf.
These are far from definitive, but are definitely suggestive.
There’s a standard explanation in game theory as to why wars or fought (or lawsuits are brought to trial, etc.), even when everyone would be better off with a negotiated settlement that avoids expensive conflict. Even assuming that it’s possible to enforce an agreement, there’s still a problem. In order to induce militarily strong parties (in terms of capability or willingness to fight) to accept the agreement rather than fight, the agreement must be appropriately tilted in their favor. If there is asymmetric information about the relative military strength of the parties, then in equilibrium, wars must be fought with positive probability.