Its hard to actually decide what you mean by peace.
When do we consider these wars began and finished, because it can be differant from whichever perspective you choose.
For China, WW2 began in 1931, however it had not been one of the major protagonists of WW1.However for them, there was also added in the communist revolutions, plus the various purges.
Poland only had a short break before it was in conflict with Russia.
The US arrived into the conflict zones quite some time after the main starts, so you can argue from this viewpoint that there was a gap.
For the inhabitant of Russia, there simply was no peave between the wars at all, from the revolution, to war with Poland to the purges, its hard to see any time of peace as far as their citizens.
For Vietnemese the ar prettymuch started in 1940 -ish and kept going until the US left.
Like the Hundred Years War between England and France, the 20c centry is well described as being one century of war with more significant periods of conflict, many of the causes of these series of actions had their roots in earlier conflicts, from empires collapsing through to huge political changes that were themselves the results of the major periods of conflict.
How likely is it that the Russian revolution would have not ocurred but for WW1? Korea was a reaction to the fall out from WW2 as was Vietnam… and so on. We can make a case for the Mid East wars being due to fall out from WW2.
I have not seen a formal study, or book that treats the entire century as a one of war with short periods of peace, but seems to me it would make a lot of sense to join up the dots.