The steamrolling tactic consists in en masse building of a few complementary armored types, and sending them rampaging straight away onto the enemy. Its sole advantage is its sheer brute firepower. It's also plain fun to smoke the enemy in an overwhelming mass of units. The downsides are, however, numerous and annoying. It is incredibly time and resource consuming, provides for completely inflexible formations, and makes easy prey for any area damage weapons. As a matter of fact, this tactic is only an option in a team game, and then only when you have already eliminated an opponent and taken over his resources.
All Factions
Tanks — This tactic makes you deploy up to 12 or more Tanks. Depending on the faction you are playing this Tank Steamrolling attack may work on various ways when steamrolling with the Tanks.
Allies
A mix of Cryocopters, Apollos, Peacekeepers, Javelin Soldiers and at least 12 Guardian tanks will offer you decent results.
Amphibious assault — On sea, swap your Ground units for at least 5 Aircraft carriers and 12 Assault Destroyers.
Mirage Tanks and Athena Cannons are another powerful option on steamrolling your enemies as well as Century Bombers.
Soviets
The most suited faction for steamrolling, as their "mass production" protocol reduces production costs by 25%. Also to their advantage is their ability to build simultaneously multiple tier 2+ factories without the need of individual upgrades. Swarms of Twinblades, MiGs, Kirovs, Bullfrogs, tanks and Artillery units will serve you well.
Apocalypse Tanks Building huge battalions of Apocalypse Tanks is another option for steamrolling but it will be expensive.
Empire of the Rising Sun
Focus on the almighty Shogun Battleship, along with some seawing and Jet Tengu support. If your opponent is out of range, try Striker units. Build 12 Tsunami Tanks, 12 Imperial Warriors and 12 Tankbusters backed up with Jet Tengu support will serve you well along with King Onis and Wave-Force Artillery.