The Baltic Wars were a series of wars between 1648 and 1714. Although there were, in fact, five, they are generally counted as a single war, as both sides were the same, as were their motives.
Angland entered the First Baltic War due to the Treaty of Dublin, which obliged it to do so. Unlike Brandenburg, Angland no longer had any economic issues, thanks to its recent gaining of Eire and Loither. Using their economic resources, Angland as able to launch a short term war in the Baltic. Though its economy was not war-focused at this point, the sheer amount of resources and men they threw into the FBW, along with Brandenburgish and Saxon talent, were part of the reasons that the war turned.
Saxony had joined the war as a result of the Instrument of Secession, signed in 1602 by Saxony, Brandenburg, and numerous other Northern German Schismist states. The treaty pledged a mutual defence pact; by 1648, however, as a result of civil wars within the HRE, of the original states only six survived. Three of them affirmed their pact, but two others remained neutral in the wars and one (Mecklenburg) sided with the Baltic Alliance. Saxony was possibly the strongest of the Grand Alliance at the start of the war, as Brandenburg was still plagued by the civil wars in Germany and Angland was destitute.
Brandenburg and Russia were the initial combatants in the war. The war came about due to the trading conflicts that emerged in the Baltic between the Gewerbe trading league of North Germany and the Torgovaya trading league of Russia. Tensions began when Russia banned Gewerb ships from their ports; Poland and Finland (this was before the unification of Scandinavia at the Treaty of Oslo) did the same, while Norway, Islafold and Sweden did the same. Danemark refused to, because the Gewerbe ships brought them trade from the Mediterranean sea. However, after the foundation of the Danish Handel League, Danemark began placing restrictions on the Gewerbe League, which was now unable to find port in the Baltic. When the Treaty of Oslo ended with Scandinavian unification, the Gewerbe ships, afraid that they might now lose their trade route out of the Baltic, struck first and attacked Copenhagen, destroying the port and almost all the Handel league ships.