Do opposing forces immediately fight upon a Declaration of War?

Question

For this question, Russia and Prussia start at peace. The sequence of events is:

1. Month 1
   1. Prussia declares war on Mecklenburg
   2. Russia gains control of Mecklenburg - Russia does not DOW Prussia in support of the minor
   3. During its land move Russia puts a depot with garrison in Mecklenburg
   4. Prussia moves a corp into Mecklenburg and drops a garrison in Lubeck
2. Next Month
   1. Russia Declares war on Prussia

Are the forces in Mecklenburg forced to fight immediately?

Answer 1

They are not forced to fight immediately. However, if the Prussian corps remains in Mecklenburg, at the conclusion of its movement phase, it would fight a trivial combat with the Russian depot garrison.