In 1962, the Sino-Soviet Republics signed a defense agreement, allowing each other to help the other country when in military conflicts. This was created due to the ongoing missile crisis and possibility of war. Cuba also aided the Communist SSR army in the Sino-Soviet Civil War, although ultimately the Communists lost, causing the downfall of the SSR.
Cuba has a relatively strong economy; it got greatly boosted after becoming allies with the SSR. Due to the fall of the SSR, Cuba is one of the strongest Communist nations on the planet. While it doesn't have a fantastic military or GDP, Cuba's economy is currently on the rise.