The people along the route to Philippi are loyal to the conspirators only because they were forced to be. When the enemy takes the route to Philippi they will likely side with the enemy to add to their numbers. Cassius goes along with Brutus. - See more at:
It is known that 2.5 Million People fought during the Battle of Stalingrad and ruffly 1.85 Million People were killed during the Battle of Stalingrad, so Around 650,000 people survived that battle 2/3 of the Survivors were Soviets.