Actually, only one of these cities would be enough to answer the question, as they both lie only on the sea: the Baltic sea.
The Baltic sea joins the Atlantic Ocean next to Denmark.
Then the merchants shipped those manufactured goods, along with the American sugar and rum, to West Africa where they were bartered for slaves. The slaves were then brought back to the Caribbean to be sold to sugar planters.
I think the main point is that Britain had its tentacles spread far and wide, meaning it was involved with a number of countries. This cartoon is Russian propaganda, so I would assume that Russia was worried that Britain was taking over and becoming too powerful.
