"Our nation is not an island. We should not be under the illusion that we will be spared from political, economic, ecological and military conflicts if we do not participate in finding their solutions," Gauck said in his key-note address at the official commemoration ceremony held in Stuttgart yesterday.
"Germany should ask itself whether it is living up to its responsibilities towards its neighbours in eastern Europe, in the Middle East and in the southern Mediterranean and whether it is doing enough to win the aspiring emerging nations to become partners on the international stage," he said.
Chancellor Angela Merkel and several cabinet colleagues, Norbert Lammert, president of the Bundestag, lower house of parliament, Andreas Vosskuehle, president of the Federal Constitutional Court, representatives of state governments and parliamentarians were present at the ceremony.
It was hosted by state premier of Baaden Wuerttemberg Winfried Kretschmann, who currently holds the rotating presidency of the Bundesrat, the upper house.
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The president said he does not want Germany to become powerful to impose its will on others.
Gauck, a former protestant theologian, who played a leading role in the peaceful revolution in the former East Germany, which led to the collapse of the communist regime 24 years ago, paid tributes to the people, who fought to liberate themselves from the dictatorship.
A mass movement inspired by a few hundred demonstrators in Leipzig contributed to the collapse of the Berlin Wall in November 1989 and the country's reunification a year later.
Chancellor Merkel, who grew up in former East Germany, said this process has not been completed and large disparities still existed between the two parts of the formerly divided nation even 23 years after the reunification.
The day of German unity celebrations began in Stuttgart with an ecumenical service conducted jointly by Catholic and Protestant churches and it was attended by chancellor Merkel, her cabinet colleagues and other leaders.
Several thousand people took part in concerts and other cultural events in Stuttgart city throughout the day.
Similar celebrations to commemorate the reunification anniversary were held in major cities across the country.