I just watched Vikings (I know, late to the party) and realised, that in the first few battles they where heavily outnumbered, at least 2:1 and still won a battle with minimal casualties.
Also the film 300 came to my mind and other films of historic battles and kingdoms. In most of these films/shows the main faction seems to win purely by being more skilled then the others, having better fighting strategies and tactics, leaving the enemy army in fear and mostly make them look “inferior”. Or they just have way better gear that makes them kind of invincible.
Is that a realistic portraiture of how battles where decided back in the good ol’ times, where you fought head to head or is this “artistic freedom”?
Numbers helped, but it's not always the case.
For instance if you take the battle of Stamford Bridge in 1066, marking the end of the viking age, the Saxon army outnumbered the Norwegian army and won, both because of numbers and with the surprise effect.
But if you look at other battles, like the battle of Stirling Bridge or the battle of Agincourt, the winners (respectively the Scots and the English) were vastly outnumbered and still won.
So overall, while numbers can be a determining factor in the issue of a battle, what truly will count is the tactics used and the environment. To take again the examples, the Scots won at Stirling Bridge because they used the terrain at their advantage by forcing the English to cross a bridge, thus creating a bottleneck (like at the battle of Thermopiles). At Agincourt, the English army was almost entirely made up of longbowmen and positioned themselves on a terrain that forbade the french knights to flank them. The terrain was muddy and thus the longbowmen could harass the knights from a distance.