Did Mexico have an agreement to have forever open borders to the States 200 years ago?

No.

Mexico and the United States have had wars of various types for two hundred years. Ever of the Mexican American war? The U.S. Marien Hymn “From the Halls of Montezuma…? Pershing’s skirmishes with Pancho Villa?

And, there has been anti-immigrant feeling towards Mexicans for over 100 years.

There is no open border policy with Mexico. Not on our side or theirs. Illegal immigration remains illegal.

Check your sources.

The U.S. comprised of 19 states in 1816, from the Atlantic Ocean to the Mississippi River, except for the State of Louisiana which sits on the other side. Beyond that, west to the Rockies and north to the 49th parallel was the Louisiana Purchase that the U.S. had bought from Napoleon in 1803, which was referred to as the Missouri Territory in 1816.

The peninsula known as East Florida was claimed by Spain, but it was not occupied by any military force and therefore was ripe for incursion by the US led by General Andrew Jackson, who eventually became the first governor of the Florida Territory. It was occupied by Cree, Cherokee, Miccosukee, Seminole and other aboriginal tribes.

The area known as the Oregon Territory (from the 49th parallel to today’s northern border of California, comprising of the areas presently occupied by the states of Washington, Oregon, Idaho and parts of Montana and Wyoming) was co-occupied by business firms and settlers from Russia, Great Britain and the US. It was in dispute, but the problem hadn’t come to a head as yet.

U.S. foreign affairs at the time were dominated by our relationship with Great Britain. We had a war with them in 1812 and we were not only suffering crippling debt, but we were being flooded with cheap British goods. We were in dispute with them about the Oregon Territory and the Michigan Territory. Nobody wanted another war with GB and these disputes were eventually settled diplomatically.

New Spain’s borders were legally closed to all. The area claimed by Spain encompassed everything west of Louisiana to the Pacific including the areas now occupied by the states of Texas, New Mexico, Arizona, California, Nevada, Utah and parts of Oklahoma, Colorado and Wyoming. This area was mostly occupied by aboriginals with a light sprinkling of administrative Spanish missions throughout. It was impossible to patrol so there were settlements by citizens of the U.S., especially from the Mississippi river basin into Texas. This irked the Spanish government, but there wasn’t much they could do, so they began to sell rights to the land and with that citizenships to the Vice Royalty only.

There were, of course, local disputes between Spanish authorities and the Americans as immigration became increasingly Anglo and protestant, but there was a common enemy to divert this violence until the late 1830’s—the Comanche.

There isn’t an agreement to have open borders, but I remember once listening to a politician in one of the border states saying he has no idea if his family came over to the US legally. He talked about how just 50, 60 years ago people went back and forth across the border constantly. I assume back then no one was keeping careful track of who returned and who didn’t.

In fact, people still go back and forth all day every day. Mostly with permission of course. The kids of one of my husband’s cousins cross the border every day to go to school.

This is the short answer:

Mexico didn’t exist until 1821, and only became an independent republic in 1824. Before that it was New Spain and was ruled by the Spanish monarchy. Neither New Spain or Mexico ever had an open door policy with any other country. But since they were unable to supply enough troops to enforce this closed door policy, the northern territories of New Spain, and later Mexico, were occupied illegally by American immigrants from the Mississippi river basin states with impunity, eventually causing the Mexican American War of 1846–48. In this way the U.S. took all the area north of the Rio Grande away from Mexico—just in time for the discovery of gold in the California Sierra Nevada. Thereafter, the borders have been conditionally closed. The conditions change dependent upon each country’s evolving needs. But even today, these conditions are difficult to enforce.