Arrange the events that led to the unification of Germany in correct sequence

Correct sequence of events that led to the reunification of Germany.

1961 - The Soviet forces constructed the Berlin Wall to prevent the escape of East Germans into West Germany.

1987 - US president Ronald Reagan delivered a famous speech challenging Soviet leader Mikhail Gorbachev to tear down the Berlin Wall.

1989 - East German leaders gave orders to open the gates of the Berlin Wall.

1989 - Newly independent Hungary opened its border with Austria.

1990 - The representatives of East and West Germany signed the Reunification Treaty.