Somehow I doubt it was all that peaceful or stable. The so-called marine merchants probably also plied their trade as pirates and privateers both (depending on your point of view). While the big wars may have been reduced in number the general lawlessness should've increased as thugs and strongman politics prevailed.
In classical times, typically, piracy was carried on by freelancers with the complicity of this or that town which let them use it as their home port. Places which made a living by fishing (for example) had times of the year when they knew commercial trade was in season, so they’d gear up for a little piracy on the side.
The monsoon winds made round trip trade in the Indian Ocean (”Erythrean Sea”) a yearlong thing (the winds blow east for months, then stop, then blow west for months, then stop...), and business in Roman times was enormous, as were the Roman merchant ships of the time; they berthed in ports along the Red Sea. Hellenistic traders operated from there also, as well as out of the Persian Gulf. Piracy must have existed, but probably wasn’t as much of a problem then, or business wouldn’t have been as good as it was.
In recent years, traces of a transplanted Tamil population brought by some Roman entrepreneur from India to a town on the Red Sea may speak of an effort to produce “imported” goods such as pottery or textiles, things with lower markup, closer to home, in an effort to cut costs.