No wonder everyone is so surprised.
At this time, so-called international trade agreements mostly involve estimating tariffs on a whim, or prohibiting/allowing certain products.
When issues arise, either a big country pressures a smaller country to concede benefits, or they start a conflict directly.
The previous Seine-Rhine Trade Agreement was already a model of such agreements, and the current common market rules are even more advanced and civilized.
At least, from the perspective of all member countries, the clauses are flawless, treating both large and small countries equally, and even favoring smaller countries.
For example, there are provisions to protect disadvantaged industries in smaller countries. The election of the Arbitration Committee also grants one vote per member country, giving Modena and France the same level of influence.
Not joining such a perfect common market would be a disservice to oneself!
And these thoughts had long been anticipated by Joseph.