Final answer:
Nixon was forced to resign because of the Watergate scandal and subsequent cover-up, where evidence from the White House tapes showed he had conspired to obstruct justice. Facing impeachment, he resigned on August 8, 1974.
Step-by-step explanation:
President Richard Nixon was forced to resign due to his involvement in the Watergate scandal and the subsequent cover-up. The Watergate incident began with a break-in at the Democratic National Committee headquarters at the Watergate office complex during the 1972 presidential campaign. Although initially, it seemed that Nixon might not be directly involved, the investigation unveiled that he and his aides participated in a cover-up, leading to several indictments.
As the investigation progressed, Nixon's role became evident when the Supreme Court ordered the release of the White House tapes, which demonstrated that Nixon had conspired to obstruct justice by using the CIA to cover up the break-in. His public approval fell drastically as these revelations became public.
The House Judiciary Committee passed three articles of impeachment in July 1974, but before the full House could vote, the tapes implicated Nixon beyond doubt. Confronted with almost certain impeachment and removal from office, Nixon resigned on August 8, 1974, after accepting responsibility for the scandal. His successor, Gerald Ford, would later pardon him, but Nixon never admitted guilt regarding his involvement in the break-in.