What is national unity?

What does it mean to have unity or be unified? We certainly don't expect to agree on everything. Even expecting an increase in agreement on issues is unreasonable. In fact wide-spread agreement causes its own problems because it leads to complacency and shutting out new ideas.
So what is unity all about? In a marriage, people talk about presenting a unified front, which usually means hiding differences. I don't think this is the right model either.
National unity is about believing in your country's citizens and leaders, believing that despite differences in opinion, we are all looking out for the good of the country. It is about maintaining a perpetually open mind and an honest interest in what others think.
World leaders learned long ago that just because you don't agree on all issues does not mean you can't form treaties on others. Similarly, some values are often cited as American values, among them freedom. These are our common ground from which we can create unity.