What was the political instability and economic changes in Europe in the early nineteenth century?

Explanation:Developments in 19th-century Europe are bounded by two great events. The French Revolution broke out in 1789, and its effects reverberated throughout much of Europe for many decades. World War I began in 1914. Its inception resulted from many trends in European society, culture, and diplomacy during the late 19th century. In between these boundaries—the one opening a new set of trends, the other bringing long-standing tensions to a head—much of modern Europe was defined

d.)   when the us left nato after the end of the cold war and they had to evolve to focus on more humanitarian measures with the smaller budget