Final answer:
Stephen Austin took over his father's efforts to settle Texas in 1821, an action aligned with Mexico's intent to populate and defend Texas, but it also catalyzed demographic and political changes, especially concerning the practice of slavery.
Step-by-step explanation:
True, Stephen Austin did indeed take up his father's cause to bring settlers to Texas in 1821. After Mexico gained independence from Spain that same year, it allowed Stephen to manage his father's grant. This was during the period when Mexico, under various governments including that of Agustín I and later Vicente Guerrero, sought to populate and secure Texas by inviting American settlers. These settlers were meant to bolster the non-Native population and provide a bulwark against further North American expansion. However, Mexico's encouragement of American settlement led to significant shifts in the region's demographics and societal structure, especially regarding the introduction and expansion of slavery which later became a contentious issue culminating in Texas' independence movement and tension with Mexico.