Hi,

The ecological imbalance is a natural or- human caused disturbance disrupts the natural balance of an ecosystem.  For eg- if species are disappear or a new species is introduced it can shift an ecosystem to a state of ecological imbalance.

The major reasons for the decline of harappan civilization are-

1. Disappearance of seals , the script, distinctive beads and pattern.

2. The shift from the standardized weight system to use local weights.

3. The shift and abandoned of cities.

4. Aryan invasion was believed to be major reasons for the decline of harappan civilization.

Many scholars thinks that these are the reasons that's why harappan civilization decline.