Reason one: the industrial and agricultural foundation is good. Cuba was a colony of Britain and America in modern times. Due to the suitable climate and prosperous plantation economy, the colonists left relevant industrial facilities here in order to effectively exploit the minerals contained in Cuba Island. Before Cuba's independence, its sugar industry, cigar manufacturing industry, machinery mining industry and other related industries were very developed, among which sugar industry and cigar manufacturing industry were world-renowned. These factors enable Cuba to obtain foreign exchange by exporting these products.
Reason 2: Brother countries help. Most countries in the western capitalist camp blocked Cuba. Under the leadership of the Soviet Union, the Eastern Group should support Cuba and continue to maintain exchanges and economic trade with Cuba. In addition, South American countries such as Venezuela and Colombia have always had close relations with Cuba. These countries are still trading with Cuba under threat, some countries in Africa and Asia have not broken diplomatic relations with Cuba, and Cuba's capital chain has never broken.
Reason 3: there is support from big countries. After the United States began to block the sanctions, the Soviet Union immediately gave Cuba all-round support to help Cuba set up factories and develop the technology it taught. Relying on Soviet subsidies, Cuba was little affected by sanctions, but the people became richer under sanctions. After the disintegration of the Soviet Union, China became a strong supporter of Cuba, and a large number of Chinese-funded enterprises settled in Havana, which made Cuba's economy develop continuously and steadily.
Internal development and external assistance have enabled Cuba to develop continuously.