King Gustav III of Sweden initiated the war for domestic political reasons, hoping to gain support from the opposition.

Despite forming an alliance with the Ottoman Empire, Sweden failed to secure support from Great Britain, the Dutch Republic, and Prussia.

Sweden's initial plan to attack Saint Petersburg and instigate a coup to depose Empress Catherine II did not materialize.

During the Russo-Swedish War of 1788–1790, Sweden attempted to prevent Russian ships from cutting off coastal sea routes by building fortifications at Hangö and on its surrounding islands.

King Gustav III of Sweden, realizing the difficulty of defeating Russia and facing mounting war expenses, sought peace.

The conflict was initiated by King Gustav III of Sweden for domestic political reasons, as he believed that a short war would leave the opposition with no recourse but to support him.

Despite establishing himself as an autocrat in a bloodless coup d'état that ended parliamentary rule in 1772, his political powers did not give him the right to start a war.

However, only the Ottoman Empire was willing to ally with Sweden while Great Britain, the Dutch Republic, and Prussia rejected efforts to form an alliance.

[clarification needed] The Parliament then decided on the creation of a National Debt Office to raise funds and finance the war, a move that gave rise to a wave of inflation of the Swedish riksdaler.

The staged attack, which caused outrage in Stockholm, was to convince the Riksdag of the Estates and to provide Gustav with an excuse to declare a "defensive war" on Russia.

Vice Admiral Wilhelm von Dessin who commanded the small Russian squadron agreed to render honours to Duke Charles but not to the Swedish flag and managed to dissolve the threatening situation and continue towards Copenhagen.

On 26 July, the coastal fleet under Colonel Anckarsvärd departed for Frederikshamn, carrying 6,000 men, while a 4,000-strong unit advanced on land under General Gustaf Mauritz Armfelt.

The Swedish coastal fleet clashed briefly with a group of Russian galleys outside Frederikshamn on 28 July, and forced them to retire within the protection of the fortifications.

Attempts to swiftly capture Frederikshamn ended in total failure for several reasons, one of the most glaring being the increasing unrest against the king amongst the officers.

King Gustav III's position, surrounded by rebellious officers, was greatly improved when news of a threat of war from Denmark–Norway became known and he could head back to Sweden on 25 August without being accused of deserting his troops.

A Norwegian army briefly invaded Sweden and won the Battle of Kvistrum Bridge, before peace was signed on 9 July 1789, following the diplomatic intervention of Great Britain and Prussia.

A small detachment, under command of James Travene, from the Russian fleet cut the safe coastal sea route past Hangö in late August 1788.

A small coastal fleet detachment under Lieutenant-Colonel Victor von Stedingk [sv] sortied to drive off the Russians, but lacked the strength to do so.

However, preparations and unsuitable weather delayed departure until 20 November, when the sea at Sveaborg was already frozen over and some ships had to be freed by sawing the ice open for them.

[24] In an attempt to prevent Russian ships from cutting off coastal sea routes, the Swedes built several fortifications at Hangö and on its surrounding islands during the winter of 1788/1789.

On the naval front, Sweden had not been so lucky; the crews of the open sea fleet based at Karlskrona suffered heavily from fever, making both fitting and manning the ships very difficult, and it took until 6 July before the fleet was able to set sail, under command of Duke Charles of Södermanland, who had the experienced naval officer Admiral Otto Henrik Nordenskjöld [sv] as his flag-captain.

In addition to the problems, the commander of the coastal fleet Colonel Anckarsvärd was arrested for being involved with the Anjala conspiracy and replaced with Admiral Carl August Ehrensvärd.

When forces moved to their winter encampments, very little had changed from the spring, with the Savolax Brigade having recaptured lost land, and only Puumala had remaining in Russian control.

Since von Rajalin's forces lacked the strength to overpower the Russian blockade, they instead covered the Swedish transports in their passage through the Barösund strait.

The Russian blockade at Porkala was after 24 August 1789 under the command of Captain James Trevenen, who started the effort to break the Swedish hold on Barösund.

Instead of blockading the town, the Swedes chose to continue further towards Vyborg while raiding Russian supplies along the coast, and reached the Beryozovye Islands on 2 June, from where it attempted to support the open sea fleet in the Battle of Kronstadt.

The Swedish escape from Vyborg Bay started on 3 July and lost several ships when they ran aground due to bad visibility in the treacherous waters.

The Russian coastal fleet, led by Karl Heinrich von Nassau-Siegen started its attack against the Swedes on 9 July 1790, in what became known as the second Battle of Svensksund, which ended in a decisive Swedish victory.

The Swedish attack foiled the Russian plans of sending its navy into the Mediterranean Sea to support its forces fighting the Ottomans, as it was needed to protect the capital, Saint Petersburg.