How to connect the elements of this sentence

Question

世界80か国で行われた国際調査の結果が発表された。

I really have problems with some semantics, grammar and parsing here.

First: 行われた. Something didn't "do" or "perform". In the overall sentence, I dont know how to meaningfully integrate this. Second: か国で I guess the か could be some kind of suffix for counting countries. で is probably the particle で here? It would somehow make sense at least in the way I understand the sentence. Third: 国際調査 "international investigation". I don't know what interpretation from a syntactic perspective would be correct. "The international investigation which didn't do/perform in 80 countries." or "The international investigation about: It doesn't do in 80 countries."

My attempt at a full translation would be: "The results of an international investigation, which didn't do in 80 countries, were published."

EDIT: 行われた is not negative form, as pointed out by lelecteur. Besides I also noticed that its passive, or better said, that I forgot to translate passive...^^ Therefore, the attempt at translation should be: "The results of an international investigation, which was performed in 80 countries, were published.

Answer 1

• You've already answered the first question; 行われた is the passive form, not the negative form.
• ～か国 is a counter for countries. This か is also written as ヶ (small katakana ケ), but it's fine to write it using hiragana as it is pronounced. For example, 1ヶ月, 1か月 and 1箇月 mean the same thing, and are pronounced in the same way. See also: Why small version of katakana ヵ is used in a word 二ヵ国語
• で right after it is the location marker, as you have correctly guessed.
• This 国際調査 might be better translated as "international survey".

Answer 2

"The results of an international investigation, which was done in 80 countries, were published."