up to 15 years, and many developed into armed conflicts, such as the Thirty Years' War (1618–1648). The war started as a war of succession to the Bohemian throne. Animosity between Protestants and Catholics in the Holy Roman Empire (now Germany) added fuel to the fire. It soon escalated to a huge conflict that involved all the major European powers and devastated much of Germany. When the war ended, some regions of the Holy Roman Empire had seen their population drop by as much as 70%. However, as global temperatures started to rise, the ecological stress faced by Europeans also began to fade. Mortality rates dropped, and the level of violence fell. This helped lead to the Enlightenment, which witnessed the emergence of innovations in technology (which enabled industrialization), medicine (which improved hygiene), and social welfare (such as the world's first welfare programs in Germany) and made life even more comfortable. North America Early European explorers and settlers of North America reported exceptionally severe winters. For example, according to Lamb, Samuel Champlain reported bearing ice along the shores of Lake Superior in June 1608. Both Europeans and indigenous peoples suffered excess mortality in Maine during the winter of 1607–08, and extreme frost was meanwhile reported in the Jamestown, Virginia, settlement. Native Americans formed leagues in response to food shortages. The journal of Pierre de Troyes, Chevalier de Troyes, who led an expedition to James Bay in 1686, recorded that the bay was still littered with so much floating ice that he could hide behind it in his canoe on 1 July. In the winter of 1780, New York Harbor froze, which allowed people to walk from Manhattan Island to Staten Island. The extent of mountain glaciers had been mapped by the late 19th century. In the north and the south temperate zones, Equilibrium Line Altitude (the boundaries separating zones of net accumulation from those of net ablation) were about lower than they were in 1975. In Glacier National Park, the last episode of glacier advance came in the late 18th and the early 19th centuries. In 1879, the famed naturalist John Muir found that Glacier Bay ice had retreated . In Chesapeake Bay, Maryland, large temperature excursions were possibly related to changes in the strength of North Atlantic thermohaline circulation. Because the Little Ice Age took place during the European colonization of the Americas, it discouraged many early colonizers, who