Research also plays a big part in a successful empire. There are two main groups of technologies to research - economic and ship based. Generally speaking, economic technologies increase the output of your industry, giving you more resources to play with, and also reduce the cost and upkeep of your ships. Ship based technologies increase the "power" of each slot you allocate, so adding one beam slot at level 10 will give the ship considerably more firepower than simply spending two slots on level 1 beam weapons.
Additionally, the relative difference between combatants' weapons and shield technology levels determines how much of the damage is absorbed by a ship's shields and how much passes directly to its hull. Some weapons, like missiles, have a "natural" shield penetration rate of 50%, but against an opponent whose shield technology is higher than the missile technology of the attacker, this can be reduced, or even completely eliminated, depending on the technology gap. On the other hand, against an opponent with a much lower shield technology a lot higher percentage of the damage is applied to the hull directly.