These teams were/are:

The Nationals/Senators of the American League. Played from 1901 to 1960, and then became the Minnesota Twins. Washington Senators of the American League, known as the ‘Nats.’ Played from 1961 to 1971, and then moved to Texas in 1972, and became the Texas Rangers.

Nationals of the National Association, in 1872 and 1875.
Nationals of the Union Association that existed for one year – 1884.
Nationals of the American Association in 1884.
Nationals of the National League, from 1886 to 1889.
Nationals of the American Association in 1881, and of the National League from 1882 to 1889.

The current Nationals team started its life in professional baseball, in 1969, as the Montréal Expos based in Montréal and became the Nationals after relocation to Washington D.C., in 2005. After their start in 1969, the team had a very mediocre decade, losing most of the time.

However, in 1981, they had their only Division win, in the split season shortened by strike, but lost 3-2 to the Los Angeles Dodgers in the National League Championship Series. As Nationals, the team has not won any Major League title.

The Relocation

From 2002 onwards, the Montréal Expos was owned by the MLB, who, after a few years, started looking for a place to relocate the team. Cities, such as Oklahoma City; Washington D.C.; San Juan; Monterrey, Mexico; Portland, Oregon; Northern Virginia; Norfolk, Virginia; Las Vegas, Nevada; and Charlotte, North Carolina, were considered. Finally, the MLB announced on September 29, 2004 that the Montréal Expos would relocate to Washington D.C., in 2005.

The Home Stadium

After their relocation to D.C., the now Nationals made the Robert F. Kennedy Memorial Stadium, commonly known as the RFK Stadium or simply the RFK, their home. Constructed at the cost of $20 million, the Stadium, then known as the D.C. Stadium, opened on October 1, 1961. It was renamed in January 1969 in honor of Robert F. Kennedy, United States Senator and Presidential candidate, who was slain in June 1968 in Los Angeles.

The RFK Stadium was renovated at the cost of $13 million, before the Nationals moved in. The Nationals are slated to remain at the RFK only until 2008, when they will move into a new home.

The new home of the Nationals will be the 41,000-seat Nationals Ballpark, being built in southwest Washington at the cost of $611 million. The New Ballpark is projected to open in April 2008.