Nationalism heightened in the 19th century and heading into the 20th century. The nationalistic fervor by people in Europe had them each viewing their own nations as better than the others, in competition with the others. This would lead to an increase in tension between the nations.
Imperialism expanded on that nationalistic rivalry by carrying their competition to other parts of the globe. The nations of Europe sought to grab control for themselves over parts of Asia and Africa. When war erupted, that also meant it would become a world war because the European nations would include people from their imperial territories in the war.
Militarism grew ever more potent as the 20th century opened. The competition between nations included a massive arms race in terms of expanding armies and navies. The nations also sided up in competing military alliances and made military battle plans as to how they might fight a war if war came. When a cause for war broke out, all those preparations propelled the nations of Europe into war recklessly.
C. The caste system is necessary to preserve social stability
The expansion plans of the Soviets led initially to the Containment policy of the early Cold War. The United States established the Containment policy which is primary to prevent the spread of the Communism period.
I hope this answers your question.
The answer is A.
Proof:
The Caddo first encountered Europeans in 1541 when the Hernando de Soto Expedition came through their lands.De Soto's force had a violent clash with one band of Caddo Indians, the Tula, near Caddo Gap, Arkansas. This event is marked by a monument that stands in the small town today.
C: