Final answer:
The first action of the United States in the European theatre of World War II took place in North Africa. This was part of a larger Allied strategy to secure a foothold in Europe and prepare for further invasions, including operations in Italy and the eventual D-Day in France.
Step-by-step explanation:
The United States involvement in the European theatre of World War II first took place in North Africa. This initial action against Axis forces in Europe was not a direct invasion into continental Europe but rather a stepping stone towards it.
The North African campaign was critical in securing a foundation for Allied forces from which they could launch further operations, particularly the invasions of Italy and France.
Following the North African campaign, Allied forces continued their military efforts against the Axis powers by invading Italy, which was considered the soft underbelly of Europe. The campaign in Italy provided a platform for the Allies to prepare for the eventual D-Day invasion of Normandy in France in 1944.
As the war progressed, the United States and its Allies confronted the horrors of the Holocaust and significant military engagements in both Europe and the Pacific theaters, culminating in the defeat of the Axis powers in 1945.