Complex sentence: The United States "National Archives and Records Administration" houses a collection of formerly secret documents compiled by Pentagon investigators in the early 1970s, confirming that atrocities by U.S. forces in Vietnam were more extensive than had been officially acknowledged.
Split into simpler sentences: The United States "National Archives and Records Administration" houses a collection of formerly secret documents compiled by Pentagon investigators in the early 1970s. Confirming that atrocities by U.S. forces in Vietnam were more extensive than had been officially acknowledged.