Probably there was no such sufficiently long period. If you are looking worldwide, you can always find some war going on somewhere. If you restrict to Europe, it is generally accepted that the period after the defeat of Napoleon
was peaceful. Indeed in the period from
the defeat of Napoleon in 1815 and Crimean war in 1853 European powers did not fight each other. But there was the Greek war of Independence, and almost
continuous Russian-Turkish wars.
(I do not count revolutions). If you take North America, there was no wars since 1920
(Mexican revolution). Of course during this period, US and Canada participated in
wars abroad. So there were long periods of peace (several generations) in large parts of the globe.
There was a long period of peace in the Roman Empire (from Nerva to Marcus Aurelius, 82 years). As Gibbon said, never before or again such a large population lived in peace and prosperity. But one has to discount the wars on the periphery of the Empire which were almost continuous.
In general, war is a favorite occupation of humans, whether we like it or not.
EDIT. In Wikipedia, there is a "List of wars" by years. You can see from it that there was no year without a war somewhere.