With that merger, a decision had to be made as to what would be the new capital.
The capital of pre-World War II Germany had been Berlin and the capital of East Germany had been East Berlin. West Germany moved the capital city to Bonn following the split into two countries.
Following unification, Germany's parliament, the Bundestag, began initially meeting in Bonn.
However, under the initial conditions of the Unification Treaty between the two countries, the city of Berlin was also reunified and became, at least in name, the capital of reunified Germany.
It wasn't until a narrow vote of the Bundestag on June 20, 1991 of 337 votes for Berlin and 320 votes for Bonn that it was decided that the Bundestag and many government offices would ultimately and officially relocate from Bonn to Berlin.
The vote was narrowly split and most members of parliament voted along geographic lines.