That's something a bit different than WW3. Afghanistan's Taliban held off the US because the nature of that war. Kind of like Vietnam. When invading a smaller country, the invaded have more to lose, and guerrilla warfare can work.
Discussion
There hasn't been a world war since the nuclear weapon was invented. I believe nuclear war is why we now see small proxy wars between the nuclear powers in country's that don't have access to those weapons. The closest that I know of is the skirmishes between India and China. But those battles only have minor casualties and end within a day or two.
The world may become more peaceful as every country gets nukes. WWIII seems far fetched.