We meet at a time of both of immense promise and great peril. It is entirely up to us whether we lift the world to new heights，or let it fall into a valley of disrepair. We have it in our power should we so choose to lift millions of poverty,to help citizens to realize their dreams and ensure that new generations of children are raised free from violence, hatred and fear.
This part comes from the address of Donald Trump at UN general assembly. I am little confused what does the thick it refer to, does it mean a word or a sentence? From my view, I think it refers to "whether we lift the world to new heights，or let it fall into a valley of disrepair".Second, why does should be in front of we? how to understand "should we so choose"?