Is this sentence grammatically correct:

Question

Before researching this topic, I already knew that North Korea and 99% of the world aren’t very fond of each other, and North Korea is accumulating more and more nuclear weapons.

Answer 1

The following may sound long winded but says all that you mean in one clear sentence:

 

"Prior to beginning my research on the topic of North Korea, I was already aware that said nation does not get along with the majority of other nations, as well as the fact that North Korea is currently amassing a nuclear arsenal."

 

 

You may want the change "does not get along with the majority of other nations" to something like:

 

"Prior to beginning my research on the topic of North Korea, I was already aware that political relations between North Korea and other nations are tense, and that North Korea is currently amassing a nuclear arsenal."

Answer 2

It's satisfactory.  Although personally, I would eliminate "more and more."

Answer 3

The word "aren't" is a contraction that should be replaced with "are not" for clarity.  There should be a period between the words "other" and "and" to avoid a run-on sentence.  The clause "North Korea is accumulating more nuclear weapons." should be a second sentence.  Also, you can eliminate the number of times you use the word "more" in the last clause. Here is your final statement:

 

Before researching this topic, I already knew that North Korea and 99% of the world are not very fond of each other.  North Korea is accumulating more nuclear weapons.