Final answer:
The growing power of the Republican Party in Texas is due to modern political issues becoming more relevant than historical allegiances, policy changes within the Democratic Party leading to lost support, and economic factors shifting voter preferences.
Step-by-step explanation:
The weakening of the influence of Civil War allegiances in Texas has led to the growing power of the Republican Party for several reasons. The first is the shift in political issues; modern concerns have overshadowed historical allegiances, meaning that a. Modern political issues have become more relevant than historical allegiances. Additionally, the Democratic Party has undergone significant policy changes, leading to a loss of support from voters who may have traditionally aligned with them, reflecting b. The Democratic Party has lost support due to policy changes. Economic shifts have also played a part, as voters prioritize their financial well-being and voter preferences change accordingly, highlighting c. Economic factors have shifted voter preferences. Lastly, a resurgence of interest in historical allegiances would not explain the growth of Republican strength; rather, it is a decline in these allegiances that has contributed to the political landscape change.