One month later, Tigerstedt was summoned by the German authorities, told that he had been declared an unwanted Russian citizen, and given three days to leave the country. World War I had started and Finland was at that time part of the Russian empire, having been ceded to Russia after the 1808-1809 war between Sweden and Russia. As another consequence of the declaration of war between Russia and Germany, the German government invalidated all German patents held by citizens of enemy nations.