There are explanations for the decentralized nature of the American political parties, which are based on constitutional or structural reasons, whilst other reasons are based upon what the political parties themselves want to achieve.
There are certainly explanations, which help to evaluate why US political parties are so decentralized based upon constitutional as well as structural factors. The American constitution itself asserts that the USA itself is a federal state that has a highly decentralized structure, although political parties did not exist when the constitution was originally put into place.
The USA is a decentralized federal state that consists of fifty states. Some of the states such as Texas, California and Florida could be viable nation states in their own right. That would be due to the size of their populations as well as their economic strength.
The individual states of the US have a great deal of autonomy in determining their own policies, laws, and activities. For the Democratic Party as well as the Republican Party considerable power can be exercised at the state level even if their respective political party does not have over all control of the federal government based in Washington D C.
The decentralized nature of US political parties is also related to the fact that the states were added to the union at different times rather than all at once.
Instead there are fifty states that agree that the federal government should only control certain policies like foreign policy, and defence (defense for American readers). Instead the Democratic Party as well as the Republican Party are decentralized in their organization so that their members can concentrate their focus upon the level of the individual states.
The only point at, which the Democratic Party and the Republican Party will focus on the federal or national level, is for the Congressional and also the Presidential elections. The two main US political parties put a great deal of effort into winning these elections, not to mention spending a great deal of money.
The point is that US political parties are so decentralized because the USA itself is such a decentralized nation state itself. It makes a great deal of common sense for the Democratic Party and the Republican Party to be organized at the state level as well as the federal or national level. The decentralized structure of the US political parties has been a feature of their organizations since they began.
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