I am going to summarize what is linked below.
Basically Satan questioned God's right to rule mankind. Since then many men have questioned God's right to rule mankind. Man tries to rule themselves, and look at the results. We have a multitude of corruption, hypocrisy, and evil, all from our leaders no less! With time, this evil world will end up destroying itself, which is what God will step in to stop, after finally proving that Mankind is incapable of ruling itself.
Matthew 24:21,22 "21 for then there will be great tribulation such as has not occurred since the world’s beginning until now, no, nor will occur again. 22 In fact, unless those days were cut short, no flesh would be saved; but on account of the chosen ones those days will be cut short."
Read paragraphs 11-18 from the following link.
http://www.jw.org/en/publications/books/bible-teach/why-does-god-allow-suffering/
Any questions I will be happy to answer, knowing full well that this is the internet :)
Also for answers to other questions take a look at these:
