Rushes are strategies, usually early-game, that use speed, suprise, and numbers to win. They are effective early-game because the enemy will not have had time to set up a proper base and their defensive capability is minimal.
Allies
Soviets
Flak Troopers and Bears - This tactic uses Flak Troopers and War Bears to quickly decimate an enemy base. The Flak Troopers use their Magnetic Mines on enemy structures and War Bears to ensure no infantry can bother you. If the enemy has managed to set up defenses however, your rush will probably fail.
Empire of the Risng Sun
Dojo Core Rush - A tried-and-tested strategy, the Dojo Core Rush involves rushing Dojo Cores to an enemy base and setting them up inside or nearby the base. Then, you pump out Imperial Warriors and Tankbusters to quickly overwlem and destroy the enemy infastructure. While not foolproof, this tactic can destroy or severely cripple an unprepared enemy.