We have access to secret recordings from the White House during the Cuban Missile Crisis. Pretty much every one of Kennedy's cabinet, all older, more experienced men, were shit-talking him behind his back. All of them wanted him to escalate and bomb the island. Despite this, he stood his ground, avoided a potentially disastrous conflict and came out with a favorable conclusion to US interests.

It was not very common to do so. Peasants were not skilled fighters and you'd need to equip them. Most medieval armies were small and consisted of full time soldiers and nobles.

The individual polities in what is now England had very small armies - a few hundred would be large for a powerful king. Really, they were best described as warbands. In dire situations, they'd call up the peasants in a levy known as the Fyrd.

When the Vikingrs arrived with the Great Heathen Army, they numbered in the thousands. The only way the English kind could match their numbers was with the Fyrd, and that would be pitting peasants against hardened Vikingrs.

So, the Anglo-Saxons struggled for some time against the Vikingrs and the polities they set up on the island, with Alfred the Great ultimately making massive changes to the way his society functioned, in order to have garrisoned forts prepared for them at all times. It worked, mostly, except for the times that it didn't, but it was more effective than what they had before.