How did the united states feel about japan joining the tripartite pact or the axis powers\?

The United States felt the Tripartite Pact that formed the Axis powers of World War II as a serious threat to its national security.

Explanation:

By the signing date of the pact, the Kingdom of Italy and Nazi Germany had already begun military campaigns against the allies. The Empire of Japan had only peacefully occupied the French Indochina, after pressing the French colonial authorities who could not count on any help from the metropolis (invaded by the Wehrmacht since June). Until then, the colonial power of Asia, the United Kingdom, had assigned military units in small numbers for the protection of their colonies, in part because most of their troops were already too busy fighting against Germany. Only the United States had been preparing to face the Japanese military threat, but they were not prepared to face a war on two fronts, that is, against Germany and Japan simultaneously.

The Tripartite Pact recognized the spheres of influence of the three original members, promoted cooperation among its members to establish a new world order and to promote the prosperity and well-being of its peoples. The Pact also ordered its members to support, by all possible means, a member who was attacked by an outside power, except those who were already at war, in this case France and the United Kingdom. With this last condition, Japan was not obliged to attack the Asian colonies of the United Kingdom, although finally it did so in December 1941. By a specific request from Japan, the Soviet Union was not included in the list of the attacking powers, for what when Germany invaded this country, Japan had no formal obligation to join the German aggression. In this way, the main power affected in practice by the Tripartite Pact was the United States, since if it entered into war with Japan, it should prepare to fight in Europe and Asia at the same time.

the answer to this question is the third option. hope this