All of these things contributed to the success and need for the pagan religions in Europe. The Greek pagan gods were a very harsh and unforgiving lot. Zeus the father of the gods along with his brothers betrayed and banished his father Kronos after he tried to devour them all. Zeus then tricked his brother Hades into being the master of the Underworld where only death and sorrow prevailed and Poseidon the king of the Oceans. He then proceeded to make himself the ruler of the gods effectively making sure he wasn’t challenged as he ruled from the heavens.
In the same way the people of the Greek and Roman empires pursued power and fame. The Greek city states warred with each other endlessly, constantly making and breaking alliances in order to gain the upper hand in the name of their respective god or gods. The two gods who were the cause of the greatest of catastrophes were Athena and Ares. Which were the gods of the city states of Sparta and Athens. Both of the city states believed that their god was superior and that they should in turn rule over the other Greek city states and all the other lesser gods.
This led to great conflicts between the two nations which in mythology is depicted by the grand arguments and betrayals that Athena and Ares committed on one another. The people always praised their gods and offered them bountiful gifts and sacrifices. They believed that in doing this the gods would grant them the ability to win any war or avoid any catastrophe. With this feeling of superiority and divine intervention they felt invincible and so always went out to carve out their empires at the expense of lives and money.
Because of all the bloodshed brought forth from the different gods and different cultures ending in wars it was necessary for the Greek and Roman city states to have gods that were strong and merciless. The people needed to know that their god would not allow any other nation or god to harm his people or disturb his domain. Anywhere where the dominant god was not of a warrior personality city states fell to more aggressive ones and anywhere that these aggressive city states went they carved out territories and imposed even greater control of entire regions. A weak god was indeed a weakness and a strong, merciless one was indeed the way to go.