NATO can help the people of the country to eliminate authoritarian regimes. This is because democratic elections in these countries cannot be undertaken. It is the responsibility of people what country they will build in their country. Where the state has influence in Russia there is devastation, and where the West there is prosperity.
If NATO is so much bothered about democracy, then it should first overthrow the monarchies in the GCC region, especially in Saudi Arabia and Bahrain. The biggest oppressor of human rights in the world right now is Saudi Arabia, which happens to be a staunch ally of the NATO.
Their main goal is not to spread democracy but security.
NATO is created in order to protect Europe from USSR.
When USSR collapsed, they lost purpose but now they have new goal, fight against terrorism.
Regarding issue with north Korea, it's problem between both Korea, China and USA.
I don't see any role of NATO in this conflict.
Problem with north Korea can't be solved with war.
If America attack them, Seoul, capitol of South Korea, will be destroyed in a few hours.
So, diplomacy is only solution here.