Were they perceived as equal in stature to royalty? On a similar level of prestige, but somehow different? Or were they simply seen as "lesser" because they didn't necessarily come from ancient, established lineages, or were elected rather than inherited their positions?
Did royal marriages or dynastic ties factor into Dutch diplomacy and statecraft at all? I know that the Glorious Revolution is the quintessential example of the projection of Dutch influence elsewhere in Europe, but I guess I'm asking in a general sense as well.
Every province in the Dutch Republic chose its own stadtholder, though they generally picked the same person. With the odd exception, the stadtholder always belonged to the house of Orange-Nassau, which was a noble family. Orange was a small principality located in modern-day France. By virtue of that, the Prince of Orange (the head of the house of Orange-Nassau) was a a proper sovereign - at least until Orange was annexed by France. A complication was that the stadtholder, even if he was a sovereign in his own right, had no sovereignty over the Dutch provinces.
Matters of precedence were important in politics of the time, and royalty always went above anything else (except the pope and perhaps the Holy Roman Emperor). So ambassadors of the Dutch Republic to other states were at first treated as lesser than ambassadors of a crowned head of state. However, the commercial and military power of the Republic meant that the ambassadors would expect better treatment. Anderson mentions that by 1645 Dutch ambassadors expected being treated on the same footing as those from Venice. By the end of the century Dutch ambassadors in Paris even demanded - and received - royal honours.
To recap: the office of stadtholder wouldn't have demanded as much respect from other heads of state as a proper head of state would, but since the stadtholder for most provinces usually was the Prince of Orange, he could expect proper treatment as a sovereign. The ambassadors of the Republic were at first treated as less than ambassadors of royal heads of state, but because of the sheer power of the Dutch Republic they eventually were treated as equal in stature.
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