Passage: In 1611–1632 Sweden was ruled by King Gustavus Adolphus, whose military reforms transformed the Swedish army from a peasant militia into an efficient fighting machine, possibly the best in Europe. The conquest of Livonia was now completed, and some territories were taken from internally divided Russia in the Treaty of Stolbova. In 1630, the Swedish (and Finnish) armies marched into Central Europe, as Sweden had decided to take part in the great struggle between Protestant and Catholic forces in Germany, known as the Thirty Years' War. The Finnish light cavalry was known as the Hakkapeliitat.

Question: What the nick name of the Finnish light cavalry?
Hakkapeliitat