What time period ended was WW1 started?

It only depends on what you are talking about and what you want to call it. War is continuous, but we give names to portions of the hostilities. Absence of war is so unusual that it is marked in history as an "era of good feeling". Modern war dates from the American Civil War, the first war fought by citizens rather than professional soldiers. WW1 was the first war fought with advanced weapons, such as machine guns and airplanes. WW2 was the first war fought by outproducing the enemy. The USA produced so many Jeeps that Europeans thought GIs were issued one along with their dog tags.

WW1 is said to have begun in 1914, but it is easy enough to trace it all the way back to March 28. 1861 and the Paris Commune. Even that was only a continuation of hostility with a memorable event.