The European Apex
It can be argued that modern European civilization reached its apex in the earliest years of the Twentieth Century. It was a high point of European power, confidence and culture. European science and technology had outstripped anything achieved by the other great civilizations. Most of the world had either been colonized or dominated by Europe. The only really important exception was Europe's overseas cousin in the thoroughly Europeanized United States.
Technology and military power were not the only elements of its dominance. Europe proclaimed and probably mostly believed that its conquest of much of the rest of the world was bringing the benefits of their allegedly "higher" civilization to more benighted peoples everywhere. The industrial revolution of coal, steam, and their associated technology had propelled it to dominance, and new advances like electricity and the use of petroleum seemed certain to push progress farther and faster. Few Europeans probably knew or appreciated it, but Planck had just discovered the quantum and Einstein relativity.
A key factor in this rapid progress must have been the century of relative peace enjoyed since the end of the Napoleonic wars. Economic and cultural connections, many believed, had made war obsolete, at least war between "modern" nations.
August 1914 shattered this illusion, and its consequences shattered European power, prestige, economic strength and self-confidence. The path to this catastrophe is the subject of Margaret MacMillan's The War That Ended Peace: The Road to 1914