The Origin was left out because there was not enough room in development, but it was planned and it is stated that the Darkspawn Chronicles happen if the Warden didn't survive. The Darkspawn Chronicles are therefore what happens if Duncan recruits a human peasant from Redcliffe, who does not survive his/her subsequent Joining.
The “dark spawn” threat was actually machine cultists who found Reaper corpses drifting in space, tried to scavenge it for parts but were compelled to turn hemselves into mindless husks. Here husks, without a Ctalyst to direct them, are driven to just kill and convert their victims into husks too. With the relay network destroyed, but not completely rebuilt everywhere, the machine cultist threat is most dire in a sub-section of the Terminus Systems, centered around Illium. To deal with this threat, a human Spectre named Duncan Ward was sent all the way from Earth. But the long FTL journey took decades off his life. He attempts to rally various factions together to suppress this threat, wth one factions having signed agreements with Shepard and being forced to abide by them now.
The “elves” are the asari. Ostracized and marginalized due to them suppressing knowledge of the Thessia beacon until it was too late, asari now largely live either a hand to mouth existence in once opulent colonies now turned to rubble with no one interested in trading with them, or they get by on Illium as peons or working menial dead end jobs.
The “dwarves” are the Krogan. Cut off from Tuchanka and thereby, any genophage cure that may have been deployed, Krogan on Illium exist in two communities - either the well respected, opulent Clan Thax, or the barely tolerated Blood Pack criminal organization.
The “Templars” are the turians - widely respected for helping win the Reaper War, but particularly fastidious about enforcing rules violently. The people they suppress most heavily are biotics - particularly turian biotics. Any biotic they come across is automatically shipped off to the distant Cabal academy where they learn their skills under the extremely watchful eyes of the enforcers.
Humans are also generally well respected for winning the Reaper War, but they are now the snobbish elites who look down on all other races. They therefore cluster in and around Bekenstein and are in economic competition with Illium.
