My first inclination would be to answer the first question with a clear "YES". But come to think of it, the causes of war really have not changed at all, or at least very little. Rather than changes, there has been a shift in the causes. The cause of war which has dominated the last 50 years was the cause of ideology. However, due to the recent end of the Cold War, this cause of war, has significantly declined and is almost trivial. The causes of war have shifted from mainly ideological ones to economic, ethnic and others. Although these reasons have always played a role as causes of war throughout history, they were in the last 50 years overshadowed by the cause of ideology. Now, with ideology not on top of the agenda anymore, these causes have regained their importance.
After the second World War the world was dominated by two superpowers; the USA and the USSR. The Cold War was a result of this division of power and of the important policy of spheres of influence. In the post WWII-era the Americans thought that the Russians were aiming to incorporate Western Europe (the US & British sphere of influence) into their sphere of influence (Eastern Europe) by supporting the communists in these countries. Their fears were enforced when a "coup substituted communist for coalition rule in Prague." (Calvocoressi, p.15)(even though this is an Eastern European Country, the fact that a coup was staged against a democratic government is reason enough to raise their fears). In this ideologically hostile environment the Cold War began. It was characterised by the arms race between the two superpowers who were eager to preserve their spheres of influence. Both developed such powerful weapons which were too dangerous to be used in practice, but which contributed to the feeling of security, because they acted as deterrent. (These weapons could be used "politically"[as deterrent] but not "militarily"[since they would bring complete annihilation].) "Each side armed itself to win a war which it expected the other to begin but for which it had no stomach and no plans." (Calvocoressi p.4)
Europe was a very stable area in the post-WWII era. All the conflicts between the superpowers, were never directly between US and Soviet troops, but in these conflicts one superpower supported one side and the other one the other side. These were staged in the Middle-East, Africa, and Asia. These Wars were "proxy" wars, which almost always began because one superpower saw its (often ideological) interests threatened. Thus they begun to support one side; for example in Korea and Vietnam, where the US feared a communist government to take over instead of a "democratic" one.
On one occasion, the whole World held its breath, as everyone thought that now the Cold War would turn "hot"; the Cuban missile crises. The stationing of Russian missiles on Cuba was seen as an atrocious provocation by the US, since it was in what the Americans had always considered as their "backyard", and they had no defence (weapons) facing that way(actually, the fact that Castro was in power was sufficient reason for them to be enraged, and they tried several times to assassinate or overthrow him). Ever since that incident, there has been an era of détente, but only in terms of arms, not in terms of ideology.
When, during the 1980´s, Gorbachev was in power, he signed several arms treaties and introduced reforms into the Soviet Union. Critics argued however, that the reforms were to radical, and they said that they were introduced too quickly. As a result to this, and of the re-unification of Germany on the 3rd of October 1989, the whole eastern bloc could be seen to move into a more liberal direction; the Soviet Union started to disintegrate. Several states declared their independence from mother Russia, for example the Ukraine, Lithuania, Belarus, Moldova and Georgia. Due to the reforms Russia fell into economic chaos. Inflation rose to four figures,...