Edward Luttwak in his essay Give War a Chance speculated that if there was a United Nations in the 1860s, there would still be UN peacekeepers stationed between the warring Union and Confederate troops on the Mason Dixon line as of this day.
If you can work out a way in which ceasefires would have shorten World War II in either the European or Pacific theatres, you have got a better crystal ball than me.
There were long interludes on the Western front; several years in which the Nazis fortified the French beaches while the Allies built up their invasion force in England. For all practical purposes, there is a land-forces ceasefire from Dunkirk to D-Day across the English Channel.
Luttwak wrote that cease-fires permit space for both sides to heal while only intensifying and prolonging the struggle once the cease fire ends — and it almost always ends.
This was true in the Arab-Israeli War of 1948-1949. It is true of the dozen of ceases fires in Gaza negotiated by the Security Council. It was true of all the cease-fires that failed in the fall of Yugoslavia with Serbs, Croats, and Bosnians who negotiated month-long cease fires where
John Stevenson studied 170 ceasefires. He pretty much vindicated the position that each side uses the lull in the fighting to regroup, rebuild and reinforce when for when the fighting starts again.
Ceasefires are perplexing in the many sided civil war in Syria. Aside from the Kurds, it is hard to work out who you want to win.
The Kurds just want to be left alone with their own country.
But Turkey is not happy about that prospect nor is Iraq.
You can work out who you want to lose territory but as for who might replace them, maybe the free Syrian army is a bit of an improvement.
There will be a bloodbath in reprisals if any of the other sides win apart from the Kurds. The Kurds are only willing to fight as far into Syria as they need to defend their own territory.