Final answer:
During the war, countries besides the United States tried to gain support through launching propaganda campaigns and offering tax-free imports to allies.
Step-by-step explanation:
During the war, countries besides the United States tried to gain support in various ways. One way was through launching propaganda campaigns (option B). Propaganda was used to shape public opinion and garner support for their own cause. By disseminating information and promoting their own agenda, countries hoped to gain allies and legitimacy.
Another way countries sought support was by making promises, such as offering tax-free imports to their allies (option C). This economic incentive was a way to win the favor of other nations and encourage them to align themselves.
Attacking opposing countries (option A) and refusing to trade with neutral nations (option D) were not typically strategies used to gain support, as they would likely alienate potential allies and hinder diplomatic efforts.