In his Farewell Address, President George Washington warned of a number of things. However, the speech has become famous for two of the warnings. One thing he warned about was the “permanent alliances” with foreign countries that you mentioned in your question. The other thing that he warned about was “the baneful effects of the spirit of party generally.” In other words, he was warning about partisanship and the idea of putting one’s political party interests ahead of the interests of the nation as a whole.
Washington believed that the spirit of partisanship could actually lead the country to fall into despotism. He did not think this was likely, but he did think that we should not dismiss the possibility that it would happen. Even if things did not get that far, he said, partisanship was dangerous. He said, for example, that partisanship
agitates the community with ill-founded jealousies and false alarms, kindles the animosity of one part against another…
This spirit, he says, drives us apart as Americans and makes us hate one another and be willing to believe the worst about one another. This is something that sounds very plausible given our current political situation and the levels of animosity felt between adherents of our two political parties.
Thus, the other thing that Washington warned about was the “spirit of party,” or the effects of excessive partisanship.