As Earth went to the stars, problems occurred. In some cases ignorance, in other cases, criminal activity...
At some point, early on the Kzinti were contacted, and they discovered a new food source. This wasn't a minor issue. Unless you like the thought of getting eaten.
My expectations are that for every few years of Star travel, you meet someone not so nice. Some are great enough to cause problems - Romulans, hence the Earth-Romulan war. The Romulans were about a century behind Earth, just starting to expand. The Klingons were about fives behind the Federation technology, which means a real problem. Dr. Carl Sagan(real world) figured out that this was the minimal separation of technological differences that would permit either conquest or a defense against conquest. Please read Cosmos by Carl Sagan, and/or watch the miniseries. Very insightful...
The point being that the Earth, and later the Federation are going to encounter problems. One, followed by four, followed by nine, followed by sixteen...