Using the 的 particle is an easy way to make a relative clause in Chinese. A relative clause is a subordinate clause that modifies a noun or a noun phrase. Imagine a short sentence such as "We talked about 3 things". Know, imagine that we want to give more information about these 3 things. What 3 things? 3 things that Chinese people couldn't anticipate before they got to America. => We talked about three things that Chinese people couldn't anticipate before they got to America.

It turns 没想到 into an adjective

Conjunction，maybe.的 has no meaning.

用在谓语动词的后面，强调动作的施事者或时间、地点、方式等。