Why did the Social Democratic Party of Germany join another grand coalition after the 2013 election?

Following the 2013 federal election, the Social Democratic Party of Germany (SPD) joined a grand coalition with the Christian Democratic Union–Christian Social Union (CDU-CSU) alliance primarily because the CDU-CSU's previous coalition partner, the Free Democratic Party, failed to reach the 5 percent threshold required for representation in the Bundestag.123

Although the CDU-CSU won approximately 42 percent of the vote—nearly securing an absolute majority—the absence of the FDP forced Chancellor Angela Merkel to seek a new coalition partner. While the Green Party was a potential option, the SPD, which had finished second with about 26 percent of the vote, entered into negotiations that resulted in the formation of a grand coalition. This agreement was ultimately finalized in December 2013 after receiving approval from more than three-fourths of SPD members in an unprecedented party ballot.231