Final answer:
The Jones Act of 1916 primarily granted U.S. citizenship to the inhabitants of Puerto Rico and restructured the island's government. The provided historical context and options do not directly pertain to the Act, as they relate to different periods and issues.
Step-by-step explanation:
The purpose of the Jones Act of 1916 was not directly related to any of the options provided (domestic slave trade, spread of slavery into western territories, international slave trade, Soviet Union, Cuban relations, or British colonial regulations). Instead, the Jones Act primarily focused on granting United States citizenship to the people of Puerto Rico and restructuring the island's government. It is important to note that by 1916, the issues of slavery and its spread into territories were historical concerns addressed before and during the Civil War, which ended in 1865.
The Jones Act reflected American expansionist interests and the strategic considerations of the early 20th century, as it followed the Spanish-American War during which the U.S. acquired territories such as Puerto Rico.
The historical context provided discusses various policies and acts meant to expand American influence, secure economic interests, and protect national interests through legislation in different periods. However, those historical references do not pertain to the Jones Act of 1916, which dealt specifically with the political status and citizenship of Puerto Rican inhabitants.