Final answer:
The United States is worried about the situation in Cuba primarily due to concerns about political stability, as Cuba's proximity and historical events like the Cuban Missile Crisis highlighted the nation's strategic importance to U.S. national security.
Step-by-step explanation:
The United States would worry about the situation in Cuba primarily due to political stability concerns (Option C), as Cuba's close proximity to the U.S. and historic events such as the Cuban Missile Crisis have shown that the state of affairs within Cuba can significantly impact U.S. national security. The historical context provided indicates that issues such as the collapse of the Soviet Union affected the Cuban economy deeply, which in turn could foment unrest or instability within the island nation, potentially leading to a geopolitical situation unfavorable to U.S. interests.
Moreover, given the strategic importance of Cuba in terms of its location and potential influence over the region, any instability or change in governance could potentially alter the balance of power, which is why the U.S. has frequently been involved or concerned with Cuban affairs.