Could a non-interference clause help countries from being stuck in wars and diplomatic nightmares?

No, each country has different priorities, needs and wants. The UN has had since June 26, 1945 to come up with a set of rules everyone would and could play by. If it could have been done I think they would have done it by now.

No.
There will still be covert operatives manipulating and sabotaging other countries, as there always were. They will not officially admit to it, they never do, but it will be, and is, happening.
(Iran was a democracy once, destroyed by a US and UK funded coup)
And of course there will always be those who will just ignore the rules (afghanistan, iraq, waterboarding).

No. There are always people/country who don’t play by the rules. In the years leading up to WWII Hitler was able to take over country by country because others felt others felt they should not interfere. Japan expanded and took over much of the region for the same reason.

There a many variants of a quote by Martin Niemöller
“In Germany, they came first for the Communists, And I didn’t speak up because I wasn’t a Communist;
And then they came for the trade unionists, And I didn’t speak up because I wasn’t a trade unionist;
And then they came for the Jews, And I didn’t speak up because I wasn’t a Jew;
And then they came for me .
And by that time there was no one left to speak up.”

A country that isolates itself ends up being isolated.

No. We have a duty to interfere when human rights are violated and when certain developments become a regional or global threat, but military force should only be used as a last resort.

In Rwanda thousands of people were murdered because of our inaction. We should learn from that. We need a world police force.

@mattbrowne I think you may have a point, but I don’t think the world will settle for a one government to look over another government so my response is no.
I think we have to think about cultural differences, economic differences and religious differences. Straight to the point we all cant get along and we all cant play nice because there will always be a bully or some one who want to force their political or religious ideologies on other.