So this is my first post here, so if u see somthing i have wrong comment on it if u can i thnk u can, oh well.
Timeline. sorta.
so the first major event im aware of is the creation of the forunners by the precursers. (the precursers are the most advanced race ever featured in the halo story). some time after their creation the forunners started a war with there precurser creators somehow (likly with numbers) the forunners anniallated the precursers leaving only one in existence. this was the Forunner-Precurser war
The next major event i know of is some time after. the Human,san shyum-Flood War. so a hundred and ten thousand years ago the humans are as advanced as the forunners (almost) and the humans are also allied with the san shyum (prophets a hundred thousand years later) while colonizing on one world the humans encounter a parisitic life form the flood. the flood soon overwelms many human and san shyum colonies but after decades (centuries? i dont remember) the humans find a cure and start fighting back almost destroying the flood. however human tactics in this somehow ignite the next major event.
The next major event is The Human,San Shyum-Forunner War. although the humans beat back the flood some of their tactic ticked off the forunners igniting a massive war. even though the humans nearly match the Forunners in tech the humans lack numbers. soon the humans fortify themselfs in massive Precurser bunkers and with the san shyum they manage to draw out the war for 30 years. after eventualy losing the war the Forunners punish the humans by devolving them into several sub speices so the humans could never inflict such a blow again.
The next event is sum wat ironic and reminds me of a game of rock paper scissors. The Forunner-Flood War. after the human forunner war the forunners encounter the flood for the first time. they didnt adress the threat untill it was out of control. the forunners failed to create a cure (as the humans did) and action after action prove to show little effect. the panic leads to the construction of the halo array witch wipe the galaxy clean of anything the flood can use as food. and when the array was fired it did just tht wipinig the galaxy clean of life. However before the detonation the forunners catologed as many DNA samples as they could and after the detonation the samples would be used to recreate the many forms of life in the galaxy u see in the halo games.
i will post another segment going into the more recent wars and alliences, if tht is i didnt somhow fail this entire thing. if i did sry. correct what u can by commenting.