The rising popularity of Germany’s Green party is increasing the possibility of it becoming a central player in the formation of the next German government. If the party enters the government, would increase Berlin’s focus on environmental policies and higher fiscal spending, though the depth of those policies and how fast they are implemented will depend on the ideological composition of the coalition. The Greens’ internal divisions and position on issues such as foreign policy could also create political instability and impede the policymaking process in Berlin. Germany will hold a federal election on Sept. 26, the first in two decades where Chancellor Angela Merkel won’t be a candidate. Because of Germany’s proportional electoral system, the election will be followed by long negotiations to form a government, which will be a coalition of two or more parties. Polls still put Merkel’s conservative Christian Democratic Union (CDU) in the first position, but...