Indian tactics (Spoilers)

I recently saw this on TV, but only caught the last 30-40 minutes or so and its been years since I've seen it previously.

When I came in, the War Wagon had made it safely across the bridge prior to the bridge being blown and separating it from the escorting horsemen. The wagon seemingly follows the ravine to meet up with the escort at another crossing.

At the point, Indians give chase to the War Wagon. They don't seem to intend on capturing it, since John Wayne/Kirk Douglas have an ambush set up. The War Wagon doesn't appear to change direction to elude the Indians either, so there doesn't seem to be any intent to get them to change direction - it looks like the War Wagon was headed towards them anyway.

So what was the purpose of the Indian attack? It got a lot of Indians killed but for no apparent change in what was going to happen anyway. Did I blink and miss something? Or... is this simply an action scene intended to demonstrate the power of the War Wagon's Gatling gun and I'm reading too much into the plot?

Thanks.