One more line of argument. IVC's military muscle. When Sarru-kin of Akkad completed the conquest of Summer, he had to starve them of their trade. So, what does he do, he invades Elam and Marhasi. Marhasi is an Indus Periphery which acted as a trade forward post. Marhasi is defeated. Now, after Sarru-kin's death, IVC marches in support of Marhasi and Elam but is defeated - defeated on field but Sarru-kin's son Rimush wasn't able to maintain his hold.
A century later, in the peak of 4.2k YBP event, Akkad is repeatedly pillaged by some random tribes - the Gutians. While they spread their anarchy, IVC makes the next move. It switches it's alliance to Lagash. Massive trade, even Meluhhan villages - everything appear at that time. And we also hear of a formal translator. This means it's a state level contact. Now, did Meluhha provide only a trade corridor or did it send soldiers to support it, it's anybody's guess. And did it send troops to stabilize the trade network from attacks like that of the Gutians, it's possible but it's beyond our current knowledge.
Now, you will ask. But, IVC is peaceful. It's not. Look at it's fortifications and stone weapons. There is a large scale military presence. But there is no bronze. Because bronze is scarce and no one let's it lying around. You recycle it whenever you find it. And when IVC had a Chakravarti Kshetra(else, you can't survive for 700 long years), it is but natural, in the IVC core you won't find any weapons except in graves or hordes which are very rare in IVC. Plus battlefields in millions of sq km are not easy to locate either.
Note: The alliance against Rimush refers to a certain Gupin. Now, a century later, Gutians come from Gupin hills and destroy Akkad. Long story short, it's possible after the fight, Gupin decided to make Akkad's life a hell - either prodded by Meluhha or Elam, or on it's own or just because it found an opportunity. And Meluhha deploying in support of Lagash need not be a coincidence. There are also theories Gutians came from BMAC area - meaning they are also Indus Periphery.