It has been roughly 70 years since World War II ended with the United States using atomic weapons on two Japanese targets, followed by Japanese surrender. The time since then can be divided into two general periods, the Cold War, from the late 1940s until 1991, and the Post-9/11 period, from 9/11/2001 to the present.
The Cold War was defined by a “bipolar” competition, meaning two superpowers dominated world politics for most of the 40 year period. The United States and the Soviet Union never confronted one another militarily during this time, but the relationship had many other elements common to warfare, including a military on high alert (including 50,000 nuclear weapons) and active espionage, or spying, on one another. Each side intervened in the politics of “third world” countries in effort to secure vital resources (such as oil and transit zones) and allies. “Hot” wars were fought in Korea, Vietnam, and military operations in Latin America and Africa were common. There were numerous “close calls” between the superpowers, indeed, many more of them than the general public knows about.
The 10 years between the Cold War and Post-9/11 period, or the Post-Cold War years, roughly the 1990s, saw a changing world economy as the digital age arrived. It was also a time of horrendous violence in place like Somalia, Rwanda, and the new countries that arose from Yugoslavia’s breakup. There were also new efforts to bring war criminals to justice with several temporary war crimes tribunals and one permanent International Criminal Court.
The terrorist attack of 9/11/01, taking the lives of nearly 3,000 people from at least 60 different countries (but mostly from the USA), created a new zone of conflict, one that was both global and in relation to a committed group of self-defined “holy warriors” named al Qaeda (and many related groups would arise as well). While that struggle against non-state actors continues, there are new and renewed tensions reminding us that the world is dominated by sovereign states (or countries). Russia, China, North Korea should come to your mind, but there can be other situations you may think of.
