Not sure how long this needs to be.
In the short term, every country, but especially the Axis (Germany & Japan) were devastated.
Japan got nuked (twice), and a good portion of the german population died. All countries took extremely heavy military losses, and the Soviet Union had tens of millions of civilians die.
The Allies (US,UK,France,USSR) gained immense power from their victory.
Long term effects of WW2 are numerous. It directly contributed to the creation of the United Nations. Germany was split up between the UK, France, USA, and the Soviets, which led to tensions over capitalism vs. communism, which led to the Cold War.
Japan, Germany, and Italy all ended up making massive comebacks in the late 20th century.
At the end of the war, the Korean peninsula (which had been invaded by the Japanese) was split between the Soviets and the USA, which led to the Korean war and the nuclear standoff with North Korea we are experiencing today.
WW2 also led to the modern warfare that is happening today, including air warfare, heavy naval warfare, the creation of the atomic bomb and nuclear energy in general, and modern small arms and automatic weapons.
