Sentence:  The dweller at p is last to hear about a new cure , the slowest to announce to his neighbors his urgent distresses , the one who goes the farthest to trade , and the one with the greatest difficulty of all in putting over an idea or getting people to <WSD>join</WSD> him in a cooperative effort . 
Meaning of the word marked with <WSD> tags:  become part of; become a member of a group or organization