Final answer:
The Soviet Union was the first and the United States was the second country to send a man into space. The provided resources do not mention which country was the third to achieve this milestone.
Step-by-step explanation:
The Third Country to Launch a Man into Space
The Soviet Union was the first country to send a man into space, with cosmonaut Yuri Gagarin's orbital flight on April 12, 1961. The United States followed as the second country when astronaut Alan Shepard made a suborbital flight on May 5, 1961.
However, the third country to successfully launch a man into space has not been explicitly mentioned in the provided resources. It is notable, though, that the Soviet Union and the United States were the primary competitors in early human spaceflight, with each nation achieving significant milestones during the Space Race. The United States eventually fulfilled President John F. Kennedy's goal of landing a man on the Moon and returning him safely to Earth on July 20, 1969.