In the years after the Cold War and the collapse of the bipolar order, the world has undergone significant changes. Chief among those changes has been a perceived deterioration of world stability, not only in terms of economics but also in terms of security. What indicators could lead one to conclude that in the years following the collapse of the Communist world, things have gotten more dangerous?

The collapse of the Soviet Union in 1991 was followed by an economic depression in Russia and the other former Soviet states. Though many Soviet citizens initially welcomed the fall of the Communists, most later became disillusioned and came to regard the Yeltsin regime as a kleptocracy (a government based on theft). Because Russia had no history of democratic rule, it was easy for the reversion to authoritarianism under Vladimir Putin to occur. It was unclear at first what direction Putin would take, but there is now no doubt that his regime has not only sponsored state terrorism in the Middle East, especially in Syria, but has engaged in "cyber-terrorism" by using social media to attempt influencing election results in the US.
The other obvious danger to global stability since 1991 is the rise of terrorism by Islamic fundamentalists. This was partly a result of the expulsion of the Soviets from Afghanistan in 1989. The US had provided support for the Afghan mujaheddin, but unfortunately this backfired with the rise of the Taliban, al-Qaeda, and eventually, ISIS.
No one knows, of course, what would have happened if the Communists had remained in power. But arguably the enormous increase in both "conventional" terrorism and cyber-terrorism is at least indirectly a result, or a by-product, of the Soviet collapse.