You have to force the high school scenario all over again, where you spend a whole lot of time together and you really don't have much alternatives so getting to know phase naturally becomes friendship over the course of time .

I think the best to do this is to have a goal and be pretty intense about reaching it, so those who share your same goal would naturally gravitate towards each other and spend a bunch of time together.

And the goal must have the following characteristics

1) It cannot be a generic such as "making money" or "become famous" because there are endless ways to skin those cats and when the hard stuff is gonna come people might be tempted to eject the effort and pursue one of the other avenues.

2) It has to be something that can be shared among the participants to the effort (in order to avoid internal conflict)

3) If you want it to be long lasting you need pretty serious competitors and enemies as well to propel the US v. THEM narrative and fuel the comradery inside the group

4)In a context where people don't have prior friendships to gravitate to, so ideally an expat area or a place with lots of influx from elsewhere so that people leave their previous friendships behind.

5) Ideally once reached the goal it has to be given back or there should be some sort of mechanism to reset the process.

So yeah...politics and sports pretty much. Starting from local all the way up to the pros, but the benefits do start at the local level, and if you cannot play then coach, and if you cannot coach then own or otherwise be the elected President of the team, and if you cannot do that patronize, but find a way to get into that locker room, where the uniqueness is represented by the scarcity of the trophy that you are all chasing as a group.

This is the non-drug version, the drug version is easy, everybody you do certain drugs together becomes your best friend for a bunch of hours.

I learned to cook. Then started inviting people I found interesting over. And they usually want to come back after eating my food :) Made most of my close friends that way. The meals become launch points for other bonding activities involving shared interests.