Sentence:  But he rejects , perhaps a little too sweepingly , the theory that disloyal and pro-Communist influences may have contributed to the policy of appeasing Stalin which persisted until after the end of the war and <WSD>reached</WSD> its high point at the Yalta Conference in February , 1945 . 
Meaning of the word marked with <WSD> tags:  reach a point in time, or a certain state or level