On 28 October 1709 Frederik IV of Denmark, the Danish-Norwegian king declared war against Sweden.

The war declaration came after the Swedish defeat at the Battle of Poltava, which resulted in a decisive victory for Peter I of Russia over Charles XII of Sweden.

In the naval enactment, a light Danish-Norwegian force of seven ships under Peter Tordenskjold trapped and defeated a Swedish transport fleet of 44 ships in Dynekilen fjord, just north of Strömstad, on the west coast of Sweden.

In the process, it overcame and destroyed a small island fort equipped with six 12-pounder guns positioned in the harbour entrance.

On account of the loss of this transport fleet at Dynekilen, Charles XII was forced to abandon the invasion of Norway and withdraw his troops to Sweden, where he was soon preoccupied with setting up defences against the expected combined Danish and Russian invasion force.