Considering that they are slowly release "UFO" evidence over the years, that would probably be the last step to basically force everyone into a global union. I don't think simply having a pandemic, war or food shortage is enough. These 3 still give a reason for nation-states to avoid joining others. Like, if you have all the food in the region, why would you bother uniting with the countries that you'll end up subsidizing food (unless the resources the country have outweighs the cost of food production AND having to govern all those complaining mouths)?
So putting on my tinfoil had, they'll probably make up an alien invasion (no, not those aliens from Mexico) incident that will encourage the countries to form a union. Those that don't get blasted from space.
Not aliens its ur own goverment leaders who do that also world is business right now lets say 2 countries in europe produce same things....right its not a energy cost efficent so they close one factory and build up one big one and bring the people to there from other country so this way export and imports are better ways controlled and its energy efficent.
And centralized food distrubution center will insure that each department get equal ammount of food to make sure there is not more then goes in waste.
World will be handled more like business and this production and warehouse kind of business will have departments and each departmemt will keep focus on their main duty whatever will be that duty we will find out for sure