For the OP:
We need AC for several reason.
1) First is transmission; to haul power hither and yon, you want the losses as low as possible. To that end, we use as high a voltage as feasible. [And that answer varies with the length of the transmission line; from 13KV to 500 KV...] To get that HV AC transmission, we use transformers, haul HV/low current AC, and at the far end use another transformer to make {typ.} 240/120VAC.
We have no easy way to get HV/high power DC from LV DC or vice versa. Until late, we had no way at all.
2) Motors. Tesla invented polyphase AC and AC motors. As compared to DC motors, AC induction motors are simpler, smaller, cheaper, easier to cool, FAR more reliable, and have longer lifetimes. They have one gotcha, below.
Now, in very recent times [~25 years..] high voltage/high-power semiconductors have become readily affordable.
With same:
3) We can afford to turn HV AC into HV DC, and transmit it; then make HV AC (and then MV/LV AC) again. This has several pluses:
a) The insulation on a powerline is for peak voltage. On a DC line, peak== average, so with given insulation, you can run a higher voltage/lower current/less losses.
b) Losses are lower. AC lines have somecapacitive losses DC lines don't
c) The "60 Hz" at both ends are independent in freq and phase. This is amajoradvantage on a line joining two grids.
4) The major gotcha of AC induction motors is they rotate at a speed fixed by the line freq. [No, I'm not going to delve in slip here....] while DC motors are variable speed.
BUT the same semiconductors let us take 60Hz AC, make DC, and THEN make AC of whatever frequency we need. The gadget is a "VFD" - variablefrequencydrive and they are DIRT CHEAP.
Yes, Tesla was a $&^#$&^ genius. I had a prof who'd met/work under him and he was in awe of him.