In the early 19th century, the ruling political party was the Democratic-Republicans. They selected their candidate through a vote of their members in Congress. This system let them control the White House for 20 years. Then the rivalry of John Quincy Adams and Andrew Jackson.divided the Democratic-Republicans into two after the 1824 elections and became Democrats and Whigs.
The California Gold Rush may be considered a pull factor, because people were being drawn to California because of the discovery of gold in that state.
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It is the states that must decide how they will ratify amendments to state constitutions, and congress that must decide the issue for the US Constitution.