A small trade and research base exists, which trades various items of goods with the aquatic population.

Of course, trade doesn't exist in just a theoretical world.

The town has become a small obscure village and the trade no longer exists.

All trade, combat, and diplomacy exist solely between the players of the game.

For example, a trade off might exist between economic growth and damages faced by indigenous cultures.

Measuring the risk precisely is difficult, because comprehensive accident statistics for the trade do not exist.

This trade has existed in the region for over 500 years.

It may be assumed that even international trade exists.

Economic trade existed throughout the Empire, due to the standing army stationed in the provinces.

No trade between cities exists, and such "business" as goes on within the city is a matter of barter.