The term Realpolitik comes from the German words meaning "realistic politics." It is used to describe diplomacy that is based on power and practicality, as opposed to ideology. Ludwig von Rochau invented the term in the 19th century, and its most famous advocate was the Iron Chancellor, Otto von Bismarck.
Bismarck used the principles of Realpolitik in order to achieve Prussian dominance over the rest of the German states, frequently using war in order to achieve his goal. In this, he was successful in unifying Germany under Kaiser Wilhelm I in 1871. A later example of Realpolitik was Hitler's annexation of the Sudetenland in 1938. After Hitler's original demands were rejected, Britain's Neville Chamberlain signed over the Czech territory in the infamous Munich Agreement in the hopes of avoiding war.
In the United States, Realpolitik was a central feature of the international diplomacy of President Richard Nixon, introduced through Henry Kissinger. Kissinger adopted the term to describe foreign policy based on practicality, such as the negotiations that preceded the opening of China. A second example was Kissinger's ability to convince the Israelis to withdraw from the Sinai in 1973 in the face of political realities coming from the oil crisis created by the Yom Kippur War.