Germany was particularly worried about the US's industrial strength and its vast resources, which could significantly bolster the Allied war effort. Additionally, the US's entry into the war meant that Germany would now be facing a two-front war, with the Eastern Front against the Soviet Union and the Western Front against the Allied forces. This would put immense strain on Germany's resources and manpower.
In response, Germany attempted to intensify and accelerate its military campaigns, hoping to achieve decisive victories before the US could fully mobilize its forces. This strategy, however, ultimately failed as the Allies pushed back against Germany's advances.