Why, after the Napoleonic Wars, there were almost no major wars in Europe for a century

Why, after the Napoleonic Wars, there were almost no major wars in Europe for a century, and then in 1914-1945. two world wars passed one after the other?

The 19th century was a century of revolutions and local wars. Many European states were transformed into national countries. This is how the unification of Germany, Italy took place, the struggle for independence in numerous countries that were under colonial dependence. It is also worth noting that all European countries were strongly focused on domestic economic development, that is, they were making an industrial revolution. The first industrial revolution was made by Britain. Then the rest of the European countries followed.