During the Clone Wars, the Acclamator-class landing craft was a large landing transport that could carry a large army. Were those crafts still used by the Empire after the Clone Wars? The only landing crafts we see in the Galactic Civil war movies are the Lambda and Sentinel class shuttles. How did they bring a large army to a planet?
I've never seen an Acclamator in use by the Empire in canon, and Wookieepedia's canon article on the ship indicates that it was not used by the Empire. This is likely because the Venator-class Star Destroyer started to replace it even before the Clone Wars ended. It was used by the Empire in Legends sources, such as Star Wars: Empire At War.
How did they bring a large army to a planet?
In canon, the Empire used the following ships of varying sizes to deploy troops:
- Sentinel-class shuttle
- Lambda-class shuttle
- Imperial Dropship Transport
- Y-85 Titan dropship could deploy four AT-ATs and four AT-STs, which in turn could carry 40 troops per AT-AT.
- Gozanti-class cruiser, capable of deploying TIE fighters, AT-ATs, troops, etc.
- Venator-class Star Destroyer (before it was phased out of the Imperial Navy)
Imperial-class Star Destroyer. Note that the Star Wars Databank says it can deploy assault units (troops):
Its belly hangar bay can launch TIE fighters, boarding craft, land assault units, hyperspace probes, or be used to hold captured craft.
We see a Star Destroyer hovering over Jedha in Rogue One in order to acquire kyber crystals from the city:
Presumably it could be used to deploy troops in a similar manner, though it's not clear if it can actually land.