What idea said that the US should expand west to the Pacific?

In newspapers and in political talk, the idea of manifest Destiny looked like a real concept, but a closer look reveals that it wasn't. The term was created by a newspaper writer, John O' Sullivan in 1845. It did not cause the US to expand to the west coast.

The 1803 Louisiana Purchase was not a deal made by Jefferson and Napoleon for any manifest destiny. The purchase gave the US an immense amount of territory. This was a beginning towards the movement to the Pacific coast.

The victory of the US over Mexico in the war that ended with a treaty giving the US most of what was the now Southwest and California. Mexico could not protect what they inherited from Spain, and in that era, a treaty giving the victor territory was commonplace. The war, by the way was not fought for the idea of manifest destiny.

The US expanded by annexing Texas, no manifest destiny there at all.

Long before any of the above, American Mormons had settled in what is now Utah, to escape religious persecution. The US government nor mainstream public opinion had little to do with this "push" west movement.

By 1849, the California gold rush was on. Thousands of Americans headed there to become wealthy miners. They did not travel to California because of a manifest destiny.

During the US Civil War Lincoln created the Homestead Act to give settlers almost free land if they improved it by farming as example. Lincoln was never a manifest destiny politician.

In summary, there is no evidence that Americans moved westward based on a slogan or that God had destined them to do so.