The Republic faced three existential threats; their severity is debated, but all were deeply interconnected:
No reliable revenue base; massive debt; inability to fund government, defense, or infrastructure. Currency collapsed ("redbacks" became worthless). Undermined credibility and development.
Mexico never recognized independence; launched raids (1842: Vásquez, Woll expeditions). Forced diversion of scarce resources to defense; created insecurity deterring settlement and investment.
Comanche, Apache, and other raids on frontier settlements. Costly military campaigns; hindered westward expansion; complex diplomatic/moral challenges.
Financial instability was likely the most fundamental—it crippled the capacity to address the other two. Without credit or revenue, Texas couldn't field effective armies, negotiate from strength, or build institutions. This drove the push for U.S. annexation (1845) as a financial and security necessity.