Campbell acknowledged during his assumption ceremony Wednesday in Germany he was taking charge of Army forces during "a time of transition" as the United States winds down its involvement in the Middle East, Stars and Stripes reported Thursday.
He said the number of U.S. troops in Europe should drop from about 40,000 to about 30,000 over the next three to four years.
Part of the reduction includes units already targeted for deactivation.
Also speaking at the ceremony, Adm. James G. Stavridis, head of U.S. European Command and supreme allied commander Europe, said the reductions will not affect the "strong partnership and alliance" with Germany and other European partners.
Stavridis and Campbell both indicated the future focus of the relationship between the United States and its European allies will be on training.