WarCraft: Orcs & Humans

I found that in this game there is one strategy that works for both campaigns and I am sure it could be duplicated for the random map games.

The strategy rest in the use of the spearmen/archers and catapults. In levels where there are no catapults just use all spearmen/archers.

Position your spearmen/archers in the row of 4 with one space in between, thus they with fully upgraded weapons would be the strong defensive wall against the enemy. Have the second row also one space apart from the second one position behind the first. This will make impenetrable defense line. Some of the units will die and would have to be replaced so keep and eye on the line. With addition of catapults it is possible to decrease each line to 2 units each and position 2 catapults at the sides. It is important to keep units apart one space if your enemy has catapults to avoid large losses to them. Catapults will kill anything on the square they hit and the neighbor squares.

This strategy could be used for attack. Just slowly start to crawl forward. Explore the forward are with infantry or cavalry units. If you find the space in the trees produce the needed spearmen/archers and catapults team to block that entry point. This slow crawl will comb the map and destroy the enemy as you will be closing from all sides.

Once demons/water elementals appear. Restrain this strategy for defense and move rarely forward unless to take control of much preferential position. Have two summoning spellcaster summon daemons/water elementals to attack the enemy.

For orcs a small contingent of cavalry units (don't need to be upgraded) should be kept in the base to deal with the invisible units that will sneak through the lines.