What is unusual about the word order in the first clause in this verse?

The order is the reverse of what is normal. Usually, the main verb precedes the subject, but here the subject  (Now all the Midianites and the Amalekites and the people of the East) comes before the verb (came together). This departure from the norm has the purpose of emphasizing the subject and setting it against what preceded. Possibly, the intention…is to show the deployment of the Midianites, who in the meantime received reinforcements for their army through the addition of Amalek and the [people of the East], in contrast to Gideon who was opposed even in his father’s house and his city, as seen in the previous passage. In light of the increase in the Midianite army the anticipation of seeing how Gideon will succeed against the Midianites without support is even greater.¹