In the US, your passport must be valid and NOT TO EXPIRE WITHIN 6 MONTHS or you will not be allowed into some countries. Even if it's close, like two days, which happened to a friend of mine. All was OK at the airport, and in Japan, on their way to Indonesia. But nope, they weren't allowed to continue on to their scuba vacation resort. Now that is a hard lesson. Research each country you are going to and double check that expiration date.
Also there is a blank page rule for your passport. What? You must have a certain number of blank pages in the back of your passport for them to stamp. Again, there is no negotiating, so find out up front. Or at least have 6 blank pages available. Yup, frustrating to say the least. Google is your friend in these matters.