Well, with modern day and the lack of an Avatar for more than 50 years, the spiritual world has been gone chaotic. Also, people have started to lose belief in the spirits and such; much like modern day situations. Also, for some reason, the bender population has been decreasing and vice versa. There is also the main fact that non-benders can use technology as much as benders can; with guns and such going around, the fact that you are a bender or not doesn't define if you are better at war or not. Sure, you've always got something when you're a bender, even unarmed... You see where I'm going with this? Kinda like benders are slowly going extinct and the spiritual world is following it's downfall. And since the spiritual world keeps this planet alive... There are many things going on with modern-day problems, but the main one is the spiritual world going out of control and fading away, bringing the entire world as well.