As I mentioned in my post on The Industrial Fantasy Age, coal as a fuel and steam power had a profound effect on our world, and can have the same impact on a Gunpowder Fantasy world. Especially in the area of commerce.
Before the industrial revolution, animal-pulled carts and sail and row-driven ships were the only method of moving goods from one place to the next. This limited the range that trade could be conducted, especially when perishable goods were involved. But as steam-power developed, and railroads expanded, commerce felt the impacts.
Roads have always been an aspect of trade networks. Roads allow carts to travel through areas that would be difficult otherwise. As the Industrial Revolution developed, especially in England, these roads became an important part of the network. But maintenance had been the responsibility of individual cities and counties. This led to inconsistent maintenance and sometimes poor road conditions.
Early in the Industrial Revolution, turnpike (or toll-way) trusts began to be established, taking responsibility for long stretches of road. Travelers paid a toll to use the road and those tolls were then used to maintain the road.
A more universal level of maintenance meant a more consistent rate of travel and allowed carts to move faster between cities and transport hubs. Merchants could move their goods more efficiently from the smaller towns to the larger cities and beyond.
Railroads were likely the most major transport improvement of the Industrial Revolution. What had once taken days and weeks to travel by horse or on foot, was reduced to hours and days. Railroads and steam engines also increased the amount of goods that could be carried from one industrial center to another.
For merchants, not only did this increase the speed with which they could move their goods, but it also gave them access to additional markets for their goods.
Sea travel before the Industrial revolution relied either on the wind and the weather or on oarsmen. Speeds were limited and ships found themselves immobilized by a lack of wind.
With the invention of the paddle-wheel (and later the steam-powered screw engine) ships gained consistency, speed and an independence from weather. Commercial trading on rivers became easier and allowed merchants to move their goods cheaper (because they don’t need to pay or feed oarsmen).
Commerce drives your nations. Not only do merchants move food and supplies from one center to another, but commerce drives the tax revenues that your nations use to fund their exploits and endeavors.
Keeping in mind how commerce will be different in Gunpowder Fantasy will allow you more flexibility in how your nations operate.
In fantasies, merchants are usually important members of society, but don’t have the reach that lords and nobles have. With access to railroads and their improved distribution, merchants become major players as part of your world. You begin to see “railroad barons” develop as they use their power to affect the world around them.