The 1810s (pronounced "eighteen-tens") was a decade of the Gregorian calendar that began on January 1, 1810, and ended on December 31, 1819. The decade was opened with a very hostile political climate around the world. Napoleon was invading France's neighbours in efforts to build a French Empire, causing a chain of global-scaled conflicts known as the Napoleonic Wars. Here, France's Napoleonic empire saw its rise and fall through events such as Napoleon's attempts to conquer Russia, the War of 1812 (spillover to America), and the Battle of Waterloo (Napoleon's ultimate defeat). Imperialism began to encroach towards African and Asian territories through trade, as the United States saw mass-scaled migration that headed westward towards the American frontier (mostly through the opening of the Oregon Trail.) Politics and wars Napoleonic Wars In 1810, the French Empire reached its greatest extent. On the continent, the British and Portuguese remained restricted to the area around Lisbon and to besieged Cadiz. Napoleon married Marie-Louise, an Austrian Archduchess, with the aim of ensuring a more stable alliance with Austria and of providing the Emperor with an heir. As well as the French Empire, Napoleon controlled the Swiss Confederation, the Confederation of the Rhine, the Duchy of Warsaw and the Kingdom of Italy. Territories allied with the French included: the Kingdom of Spain, the Kingdom of Westphalia, the Kingdom of Naples, the Principality of Lucca and Piombino, and Napoleon's former enemies, Prussia and Austria. Denmark–Norway also allied with France in opposition to Great Britain and Sweden in the Gunboat War. The French invasion of Russia of 1812 was a turning point, which reduced the French and allied invasion forces (the Grande Armée) to a tiny fraction of their initial strength and triggered a major shift in European politics, as it dramatically weakened the previously dominant French position on the continent. After the disastrous invasion of Russia, a coalition of Austria, Prussia, Russia, Sweden, the United Kingdom, and a number of German States, and the rebels in Spain and Portugal united to battle France in the War of the Sixth Coalition. Two-and-a-half million troops fought in the conflict and the total dead amounted to as many as two million. This era included the battles of Smolensk, Borodino, Lützen, Bautzen, and the Dresden. It also included the epic Battle of Leipzig in October, 1813 (also known as the Battle of Nations), which was the largest battle of the