The three branches of the elven race (High elves, Wood elves, and Dark elves) never divided due to a giant civil war. Instead, the splits between the three are largely philosophical, and while it has risen to the level of violence on occasion, they are able to coexist… sort of.
Both the High elves and the Dark elves are able to cross the barriers between worlds in very distinct fashion. High elven cities exist in both the Prime and the Feywild, while Dark elven cities exist in both the Prime and the Shadowfell. High elven cities shift into the Prime at dusk, and remain there throughout the night; come dawn, they shift to the Feywild, and remain there throughout the day. By comparison, Dark elven cities exist in the shadows- when the sky is obscured by clouds, during eclipses, at these times the Drow portion of the cities fade into existince, disappearing at the touch of direct sunlight or moonlight.
All three subraces build their cities in the same locations, taking into consideration one another- which is to say, during sunlit days, Wood elf city will seem sparse and curiously spread apart, only to have the conditions met for the others to appear, filling in the spaces in a way that is both seamless and distinct: each race has their own architectural styles, yet where they touch they do so with gaps or overlap. It is also said that while High elf cities are easily accessed via their predictability, there are places in Wood Elf cities kept in permanent shadow so as to allow for travel to Dark elf lands.
The main philosophical point of contention between the three races revolves around death. The High elves are functionally immortal by virtue of the energies of the Feywild- while they can be killed, so long as they remain in the Feywild they cannot die of old age (meaning that once a High elf reaches the end of their natural lifespan, they tend to remain in the Feywild during the day). The Dark elves, being followers of a god of death, find this state of affairs to be unnatural, and individuals have taken it upon themselves at times to ‘fix’ the issue in regards to particularly long-lived High elves. As one might expect this is not appreciated by the High elves. To some degree of irony, the Shadowfell is the realm of the dead, meaning Dark elves who die of old age similarly find themselves unable to cross back into the Prime.