I've read that what rookies rank up into is random, and I know that there are specific plot-related missions.
After I returned from a mission I saved the game. I then went through the process of the normal between-mission activities and then went to select my next mission. I was alerted of alien abductions in three countries
- China: Easy
- Brazil: Very Difficult
- Canada: Very Difficult
I decided I didn't really like my options all that much and hit reload. I went through and made the same post-mission decisions/assignments/purchases as I had before and again went to select my next mission. I was presented the same three countries and difficulty levels as my options.
I reloaded again. This time, I changed my post-mission actions. Even still, I was given the same three options for missions.
Clearly, the next missions offered up are not completely random. So what, if anything, affects those choices?
I'm not so much concerned with the difficulty levels like this question, but more the general mission parameters.