Why do third parties usually not last very long in the american two party system?

Third party systems have a difficult time competing against the Democratic and Republican parties for multiple reasons.

1) Lack of funds- Running political campaigns is extremely expensive. On a yearly basis, the Democratic and Republican party spend millions of dollars to help their candidates win office. Third parties have a difficult time raising this type of money.

2) History- The modern day Republican and Democratic parties have been around for roughly a century. People are familiar with their view, understand their platform, and are familiar with important individuals within the party. A third party usually struggles with these factors, as their new emergence comes at a time when a significant amount of Americans are already aligned with a specific party.

1. they could both use a veto to cancel an action.

2. women couldn't vote in the roman republic but could in the united states

i think it is the byzantine empire