Looking at Demacia's trade with Shurima, the most important part was the large-scale, high-priced export of surplus grain from the homeland.
In the past, Demacia's high-quality grain had never fetched a good price because of shipping costs and purchase prices. Despite suffering enormous losses, after the grain was delivered to port cities in Northern Shurima, local merchants bought it for just enough to break even. Over time, the Demacians naturally lost interest in taking part in international trade.
However, with the use of Ningwu Dao, Jarvan IV and the Demacian Nobles finally realized that grain shipped from Demacia to Shurima did have a price advantage. Its cost was still considerably lower than that of grain produced locally in Shurima. It was only because the port cities of Northern Shurima paid far too little for Demacian grain, and Demacia had no local sales or distribution channels, that its grain appeared uncompetitive.
In other words, shipping Demacian grain to Shurima to sell was actually profitable. In the past, local grain merchants had pocketed that profit, making Demacia feel there was no money in the trade.
So when Demacia used force in the Nashramae Campaign and flexed its muscles, it was also hoping to open up the Shuriman market.
Demacia had no interest in the barren Shuriman desert, but after ten years of trade with Shurima, its royal family and nobles had become very interested in the market for commercial grain there.
And after the Nashramae Campaign, Demacia did indeed succeed in expanding its grain market. Grain shipped from Demacia was distributed in Nazumah, then sent along the eastern, western, and southern trade routes, reaching deep into Shurima. Its profits were still fairly limited for now, but if Taric could find another route like Ningwu Dao, that would mean another golden trade road.