Why did Native Americans never unite against the European colonization that sweep them away from their ancestral lands?

Asking why Native Americans didn't unite against the Angrej and Ispans is the equivalent of wondering how Immortan Joe's “army” in Mad Max would've fared against a Scrin invasion.

1- Most Native Americans died long before they ever saw a Firang. 95% were dead of disease, either intentionally or unintentionally spread by Colonialists within a few decades of Contact.

2- The ensuing breakdown of Social Order and Civilization was so vast that we weren't aware of massive cities and nations until recently. Vast complexes once dotted the Amazonian basin but the once-civilized survivors regressed to Hunter Gatherers so comprehensively that we looked at the place as a pristine wilderness until Satellite imagery grew advanced enough.

3- We know that massive urban complexes such as Cahokia existed however such Native American structures, unlike Meso American ones, were primarily built in flood plains of rammed earth. Not only do they require more maintenance than stone, we know that floods can destroy them quickly. Consider Wheeler's studies and the Shastras which point to massive floods around 800 BC devastating cities across the upper Ganga valley. We see that urban Civilizations, when they collapse, spark chain reactions ranging from economic depression to mortality spikes. Ward-Perkins analysis of the fall of Rome demonstrates how fast and comprehensive such collapses are.

4- 10th Century Malwa had Automatons and were considered the finest builders of Bharata. Raja Bhoja's Great lakes were the largest man-made water bodies in history till Hoover dam. Yet near-constant warfare with the Peacefuls, Conquest and Desolation, and the joys of Angrej and Republic Raj ensured that this once-major centre of political power became a heap of poverty-stricken dacoit-haunted villages until recently. In 550 CE, Pataliputra was a wonder of the World, possibly the largest city ever built by man. By 600 CE, it was a ruin populated only by a handful of monks.

Moderners drunk on hedonism and the dubious wonders of their technology, fail to respect the inevitability of Collapse and the End of all things.

Imagine a great City by the banks of the Missippi, a metropolis to rival immortal Prayaga or high-walled Kaushambi. Imagine streets of rammed earth and lined canals and sun-baked houses, flanked by gardens where is sold the produce of a hundred villages. Imagine spearmen and heralds, poets and gardeners, kings and magistrates.

Imagine plague. A city of 100,000 men, women, and children- all but wiped out almost overnight, suffering the most terrible afflictions. Imagine the survivors stumbling from door to door seeking food and medicine and hope. There are no soldiers to restore order; the survivors first thieve and then slay. There are no merchants; there is nothing to buy or trade. There are no farmers; the villages are littered with the dead and dying, same as the city.

The winter is terrible. Wolves and Bears stalk the crumbling snow-blanced ruins as mothers struggle to give their dying kids warmth. Men look askew at each other, each wondering who carries the taint of disease. The canals are silting up but the last engineer is dead. The gates are crumbling but the last stonesmith fled the city. The strongest- or meanest- calls himself King; he is slain by another, and so forth. There are no guards. There is no law. Mist-haunting and Moon-weeping, ghosts and grief haunt the survivors of a once mighty town.

Spring comes with fresh rains. And floods.

The few families left flee to the forests from whence Man had once emerged. The forest feeds them. The forest clothes them. The forest comforts them. They forget the taste of bread and the shine of gold. Their children forget the songs of distant lands and the music of armies. Their grandchildren forget that once where dwell marsh lizards, there once stood a shining city that ruled over territory that dwarfed Angrejistan.

Their great grandchildren meet the Angrej, keen-eyed and steel-armed- black with soot, yellow with gold, red with the blood of a hundred peoples.

Thus was the fall of a Nation.