4 player chess with Flags - how to have alliances arise during the game

I thought it would be fun to have a set of rules causing alliances to arise during the course of the game. This is my proposal:
We introduce two white Flags and two black Flags.

The colour of a Flag is important, but not related to the colour of any army.
Any army can capture any Flag. A Flag has no own movement.

Stones are dead objects that must be captured as they are initially blocking access to the Flags.

If one player manages to capture a second Flag, that player immediately wins the entire game, provided that he or she has no King left in check. (As a consequence, each player will probably
try to capture at least one Flag. Or we could alternatively assign a huge amount of points to capturing a Flag.)

If a player captures a Flag, that Flag must be placed on that player's side of the board, so it's colour remains clearly visible to all players.

If two players - say player A and B - have captured a Flag of the same colour, than from that moment their armies are immune to each other. Their pieces can no longer capture each other or
give check to each other's King. This condition remains until all remaining players are out of the game, or until the game ends in another way.

So this way, players become allies, and can only start battling ech other after slaughtering all other armies first.
(But a player who is bound to an alliance, can still trick his ally and
take the win by capturing a second Flag.)
Long-term strategy or immediate tactics could make a particular player prefer a particular other player to team up with.

Very interesting proposal!

The introduction of a new figure - flag is very intriguing!

I am impressed by your creativity!

Sounds interesting 

What I'll do is try with phyiscal board and pieces and report back if it is playable.

Try it and report!

yes im curious too ! (even it at first it just seems to simplifying the game)

How about introducing sharks with lazers in the board, who randomly zap a piece out of exixtence?

COOL I WANT THAT PLZ LOOK AT THIS ARTICLE chess.com

or power ups that randomly spawn on the board?

 I suggest you play some 30 seconds chess games  right away. I have prepared traps for your sweet sharks!

I prefer 30 minutes, or even 30 years games @venue

30 years with sharks in a shared pool ?! Oh, that's not for me! 

We really need also to add a Boss King. Players must checkmate him 5 times to kill. It also takes up 4 squares on the board (2x2) and every 10 moves jumps to a random place on the board crushing the pieces over there.

I think the fun in 4 player chess comes from the nature of 4 individuals making independent decisions that affect the course of the game. This just simplifies the system to two parties again which isn't as interesting. 

Hmm... I wish there was this in chess.com

Bug- if red owns two flags (white+black) {blue is dead} green has black...yellow has white. Red now can't go to war and could spam queens with pawns. This would make a weird condition. Does red have all or no alliances?

turns into 4 player teams