In June 1942, the United States expanded its involvement in World War II by declaring war on Bulgaria, Hungary, and Romania. This formal declaration came as a result of these nations' participation in the Axis alliance, and it marked a pivotal moment in the U.S.'s military engagement in Europe. The declaration followed a lengthy discussion among U.S. military and political leaders about the escalating threat posed by Axis powers, particularly after the bombing of Pearl Harbor and the subsequent mobilization of U.S. military forces in response to Axis aggression.

Bulgaria, Hungary, and Romania had joined the Axis as allies of Nazi Germany, participating in military operations that supported German advances throughout Europe. The U.S. Congressional vote was overwhelmingly supportive, with few dissenting voices, reflecting a public and political consensus about the need to confront Axis powers aggressively. This declaration not only solidified the U.S. stance against these nations but also aligned American military resources against common foes in the theater of European warfare.

The declarations facilitated further military planning and operations against these nations and contributed to the overall tactical coordination of Allied forces. By broadening the scope of its war targets, the U.S. aimed to disrupt Axis supplies and communication lines critical for their war machinery. The war declaration was thus a strategic move to enforce the siege against Axis influence in Europe, directly impacting the course of military engagements for the Allies in the subsequent years.