Klingons, Vulcans, Remans
The Klingons rule the Klingon Empire and have closed their borders to the Federation. The Klingons were involved in a massacre seven years before the series, which caused the Federation to stop all aid. In retaliation, the Klingon Empire has begun to build up its weapons systems and territories in order to match the Federation. They have also begun to annex some planets located between the Federation and the Empire, including the frequent freight stop of the Yorktown in the Organian system.
The Vulcans have also closed off their borders, however, they still send ambassadors to the various Federation planets. Vulcan society was reformed 75 years prior, and their leader, Minister T'Pau, thought quiet reflection and education on the true works of Surak, the "father of logic," was necessary. Only recently after the series begins do they allow outsiders to vist their planet. Many Vulcans, such as Skon, command freighters and ships, but only to further the cause of planet Vulcan. Some Vulcans have chosen to live off their homeworld, and many of these expatriates live at the Vulcanis Lunar Colony on Earth's moon.
During the Romulan War, a group of Reman shock troops were stranded on a planet not far from the solar system. These Remans wait patiently for 70 years until they are discovered, not by Romulans, but the crew of the SS Yorktown.