I read that the British broke the last defense line of the German west front in the summer of 1918, which led to the german offering armistice. Why did the Entente powers accept it, and did not push for an invasion of Germany and unconditional surrender like in WW2?
The Germans did unconditionally surrender, this ended WW1. After that the treaty of versailles was made up which included things Germany wouldn't have agreed with (probably). They called it a diktat, because it was forced (dictated) on them.
Edit: it was officially an armistice which the Germans agreed to by believing it was to be based on Wilsons 14 points.