Among the countries listed, Germany is often cited as having long-term success with adopting democracy, particularly after World War II with the establishment of the Federal Republic of Germany (West Germany) in 1949, which became a stable democratic state.
While Liberia was founded by freed American slaves and had connections to the U.S. Constitution, it has faced significant political instability and conflict. France has experienced multiple republics and regimes, often struggling with democratic stability. Spain transitioned to democracy after Franco’s dictatorship but has had challenges as well.
Thus, the most appropriate answer is Germany.