Without going into homebrew or Wish territory (as the former is table-dependent and the latter is DM-dependent), Finger of Death creates an undead that is permanently under your command.
Being a 6th level spell, a 20th level caster can cast it six times per day (by spending all their higher level slots casting that spell exclusively), which means that, provided you have a steady supply of humanoids to cast the spell on, you could have six undeads per day, or 180 per month. In a year, that’s 2190 undeads, which is itself a small army. Give it some time, and you’d have a small country following your commands.
At that point there are only two problems: time itself (which can be solved with features that increase your lifespan, such as Boon of Immortality), and other people trying to stop you (which can be solved by using your spell slots to make them regret their decision).
Without going into homebrew or Wish territory (as the former is table-dependent and the latter is DM-dependent), Finger of Death creates an undead that is permanently under your command.
Being a 6th level spell, a 20th level caster can cast it six times per day (by spending all their higher level slots casting that spell exclusively), which means that, provided you have a steady supply of humanoids to cast the spell on, you could have six undeads per day, or 180 per month. In a year, that’s 2190 undeads, which is itself a small army. Give it some time, and you’d have a small country following your commands.
At that point there are only two problems: time itself (which can be solved with features that increase your lifespan, such as Boon of Immortality), and other people trying to stop you (which can be solved by using your spell slots to make them regret their decision).