Today marks the 19th anniversary of German Unity Day (Tag der Deutschen Einheit). It is held every year to remember when the Federal Republic of Germany and the Democratic Republic of Germany united to create one single, federal Germany on October 3, 1990.
Following World War II, the area that was Germany was divided into four military sectors controlled by France, the United Kingdom, the United States and the Soviet Union. On May 23, 1949, the sectors controlled by France, the United Kingdom and the United States became the Federal Republic of Germany. On October 7, 1949, the sector controlled by the Soviet Union became the German Democratic Republic.
The two countries developed very different political and economic systems and, due to the political tensions in post-war Europe, there was little contact between the inhabitants of the two countries. A protest against the German Democratic Republic's government occurred in Leipzig on September 4, 1989. More demonstrations took place across the German Democratic Republic.
The protests called for political reform and to open the borders. On November 9, 1989, the checkpoints between the two countries were opened and people were allowed to travel freely. This date marked the "fall" of the Berlin wall.
These events lead to political change. Democratic elections paved the way for unity in the German Democratic Republic on March 18, 1990. The "Treaty of Unification" was signed by both countries' leaders in August that year. Finally, Germany's unification became official on October 3, 1990.
(Source: Time and Date)