by MightyThor
Risk rules over the world and over the years are not 100% consistent.In earlier versions of Risk also the defender had a max of 3 dice. Since a tie favoures the defender, the defender had a huge advantage (at least if defending with 3 units). Then they "toned down" the defence to a max. of 2 dice. Still, the defender has a (now slighter) advantage (in the standard case 3 (A) vs 2 (D) dice).
In my childhood we played it like the "Brass Pigeon": Attacker rolls first, then the defender chooses how many units (two or only one) he commits to the battle. This makes the defender very powerful.
Nowadays, in times of "globalization and harmonization", there is a standard rule:
1.) Attacker decides how many (available) units he commits to the battle (min 1 - max 3)
2.) Defender decides how many (available) units he commits to the battle (min 1 - max 2)
3.) dice are rolled (which is now in fact "simultaniously")
With these rules, it is always best for the defender to roll 2 dice, if possible (I think).
(Also the "fortification/maneuver rules have chanced a lot over the years/across the versions).