Unity changed the territory of the Federal Republic as it then existed.
Two German states were founded in 1949. Before reunification, the Federal Republic therefore did not have the same territorial extent as today. The answer 1990 refers to accession and the end of that state division.
Both German states and the four victorious powers of the Second World War participated in the Two Plus Four negotiations. They settled the external conditions for unity, including the final borders and renunciation of territorial claims.
The other three answers
None of the three earlier years identifies reunification.
1933.
1933 predates the foundation of the Federal Republic and GDR in 1949. It is not when the reunified Federal Republic acquired its present extent.
1949.
1949 is the Federal Republic’s founding year, but not the year of its present territorial extent. State division continued afterwards.
1971.
In 1971 the division into Federal Republic and GDR continued. That year precedes reunification and is therefore not the answer sought.
One year does not replace every separate international-law step.
The Two Plus Four Treaty was signed on 12 September 1990 but entered into force on 15 March 1991. Four-Power rights were suspended for the intervening period from unification. More detailed questions about treaties require distinguishing these steps.
The question concerns Germany’s borders and territorial extent as a state. Changes to municipal or administrative boundaries are a different level; the catalogue answer is not a statement about every local boundary line.
Unity and Two Plus Four · Federal Government ↗Present national territory: unity in 1990. Check treaty entry into force separately.
Connect the answer to the event rather than to any year appearing on a treaty page.
Three words for this question
- das Staatsgebietnational territory
- The territory belonging to a state.
- der Gebietsanspruchterritorial claim
- A state’s claim to a particular territory.
- die Souveränitätsovereignty
- A state’s self-determination in legal and political terms.