Why did washington warn against political parties

He warned about political parties because he thought they would tear the nation apart.

He was greatly concerned that they had previously, and would again, grow seeking more power than other groups to the detriment of the whole.

Washington was aware that other governments viewed political parties as destructive because of the temptation to manifest and retain power, but also because they would often seek to extract revenge on political opponents.

He viewed this to be detrimental to the young country as an entire nation.

He also saw the dangers in sectionalism (North vs. South) and warned that political factions gaining enough power could seek to obstruct the execution of the laws that were created by Congress and could prevent the three branches from properly performing their duties as outlined in the Constitution.

President Washington expresses genuine concern in that "the alternate domination" of one political party over another, thereby allowing one party to enjoy temporary power over the government that would use it to obtain revenge on the other.