In this task, you are given two sentences in the English language (Sentence 1 and Sentence 2). Your task is to identify the connecting word between the two sentences.

Sentence 1:Shortly after the crusaders ' departure , Isaac II Angelos broke into the lands under the rule of Peter and Asen . Sentence 2:However , he could not defeat the Vlachs and Bulgarians who avoided a pitched battle , forcing the emperor to start to retreat .
however