Who is the Democratic Party rival

Republican Party

Explanation:

The Democratic Party believes in "liberal philosophy" while the Republican Party believes in "conservative philosophy."

The liberal philosophy protects the federalists' belief that more regulation is needed in order for the government to provide universal service to all. On the contrary, the conservative philosophy protects the anti-federalists' belief of having less regulation, free market and a smaller government.

The Democratic Party supports tax cut and believes that the government should be responsible in spending while the Republican Party supports higher tax, which will be used to provide service to the poor people.

The Democratic Party opposes gay marriages while the Republican Party upholds it.

These are just some of the examples on why the "Republican Party" is considered a rival of the "Democratic Party."

the name of the theory is landmass theory.