Movies from Hollywood are usually released here in the US first, or at least at the same time in theaters. This is similar with a company starting first in their home country with a product or store before going to other countries. But occasionally the opposite happens.
Avengers: Endgame opened in China before the US. It opened a couple of days earlier there. In fact, it had over $100 Million in China at the box office (not the studios take) before it opened in the States.
To go international first is unusual but to add to that in China is even more strange. China is a huge market that can show a lot of promise.
Unfortunately it is also a minefield of problems. First, the government regulates heavily, both content and competition. They limit films from outside of China heavily or pit them against each other pushing them back and opening them on together on a week that no big Chinese films are opening. Next, while the net theaters pay for rentals is about 40-50% of the box office gross, but in China it can be as low as 20%. This means that, depending on how the foreign distribution is negotiated it will make far less of a percentage for the studio than other markets.
What made Marvel choose this route? Here are a few factors I believe were considerations. First, piracy, it is a problem in China, like everywhere else but can be even more so. With the fear of such a big movie being leaked from western releases they might have wanted to get a jump on the problem. Also, they may have wanted to give it a bit of an advantage because of recent releases from Lucasfilm (another Disney owned company) Solo, which came from the huge franchise of the Star Wars universe. It didn’t do as well in China as they hoped. It bombed everywhere but China was one place they thought might save them in Solo’s case. Last, I believe they wanted to also get ahead of the Chinese Labor day (May Day) as movies are relesed on Wednesdays in China. Since May Day is Monday April 29-Wednesday May 1st, they probably wanted to jump into the week before and get as much of those days off as possible when it came around the next week.
In the end Endgame had a huge opening weekend around the world bringing in over 1 Billion in that time, the biggest ever, and snashing a number of records. So, their approach to go international didn’t hurt them and may even have made them tens of millions more in revenue because of it. And even though this movie was known that it was going to be big, it didn’t rest on that fact and still put in the work to maximize every ounce of profits it can make from the movie. I don’t see a lot of other movies taking this approach as it would not work out the same way.