They didn't; they just outlawed slavery on Mexican territories.
See related questions for further explanation.
In 1830, Texas belonged to Mexico. The Mexican government encouraged Americans to move there and settle.
French settlement.
In 1830 Mexico feared that the Americans would try to make Texas a part of the United States.
The Mexicans were worried about the great influx into Texas by Americans
Texas belonged to Mexico from 1821 to 1836. When Mexico won it's independence in 1821, it included Texas as part of its nation. Texas won its independence from Mexico in 1836 and remained independent until its annexation into the US in 1845.
The effect is... It increased tensions between Texas and Mexico.
The law of April 6, 1830, was passed in Mexico and aimed to restrict further U.S. immigration to Texas. It also prohibited slavery in the region and required foreigners to convert to Catholicism. These measures were intended to strengthen Mexican control over the territory.
Slavery (it was banned in Mexico since 1830).
Slavery is a nasty thing. Mexico's father of independence Miguel Hidalgo abolished it at the beginning of the struggle for Mexican independence (1810) but it was never officially put in any legal document until 1829; on 1830 it was approved by the Mexican congress and became a law throughout Mexico and its territories.
Ten years after Americans began settling in Texas, which started around the early 1820s, Mexico enacted stricter immigration policies in 1830 to curb the influx of American settlers. This included prohibiting further immigration from the United States and increasing taxes on imported goods. The Mexican government aimed to assert more control over the region and promote the assimilation of existing settlers into Mexican culture. These measures ultimately heightened tensions, contributing to the Texas Revolution in 1836.
Antiquities of Mexico was created in 1830.
Mexicans in 1830 were against slavery and abolished it in the Decree of April 6, 1830.