To me, unity means that though any two people may not agree on XYZ political, religious, social, or other matter, no matter how severe, they still CHOOSE to be friends.
This is something we can all do!
The only thing we NEED to agree on to have unity is peacefulness. Physical and verbal and even (the hardest) emotional peacefulness, and we can achieve unity!
Q2: What's gaming got to do with it?
See, when we sit down to game, we don't think "Oh man, I can't trade sheep with Alice because she voted for XYZ." or "I'm gonna get everyone to gang up on Fred because he's XYZ religion/ethnicity/political-leaning." Rather when we sit down to game we put the complicated issues aside and spend quality time together, appreciating each other for their shared humanity. At those times it's only Orcs, remaining HP, and Victory Points that are reasons to argue ...and I think that's a huge step in the right direction.