Final answer:
Stephen F. Austin built his first colony between the Brazos and Colorado Rivers, introducing a significant population that cultivated the cotton industry and invited the practice of slavery.
Step-by-step explanation:
Stephen F. Austin established his first colony between the Brazos and Colorado Rivers. This significant establishment occurred when Austin, adhering to his father's dying wish, led 300 families into the Mexican province of Texas in 1821, a pivotal year when Mexico gained its independence from Spain. The strategic location between these two rivers offered fertile soil suitable for cotton plantations and was conducive to the introduction of slavery, a practice later contested by Mexican law.