I like the concept a lot, looking at human from a grander point of view, integrating anomalies and various organizations into the perspective. However, the part where human and other species reached consensus and stopped the war seemed a bit too optimistic, given how we haven't been able to handle conflicts between even different groups of people for millennia.
I can imagine it's hard to make in convincing, but that part is like the climax of the story. Maybe go more into details on how the shift in people's attitude happened. Even after the war has stopped, there will still be lingering fear, doubt and hate. That can be a direction to explore.
A minor nitpick:
They could go as far as changing their own physical density, … or turning themselves as dense as diamond.
Diamond has a density of 3.52 g/cm^3, half as dense as iron, typically at 7.8 g/cm^3. Also, aluminum's density is 2.7 g/cm^3, titanium around 4.5 g/cm^3, water is 1 g/cm^3. I'm not sure if what you're trying to convey will be clear to everyone. Maybe use a more common material for reference?