The war between the Kree and Skrull is a story written by Roy Thomas. The war is a notable story because of it's enormous cast of characters and use of metaphor. It's also the introduction of the Vision and Scarlett Witch romance, which became an ongoing theme for the characters. A lot of critics consider this chapter a highlight of it's comic era and if you haven't read about it yet it's most certainly recommend it!
In this story the avengers, Captain Marvel and Rick Jones (a character on which we will come back in a other post soon!) find themselves in the middle of an intergalactic war between the Kree and the Skrulls. Earth is positioned halfway between the home galaxy's of the Kree and the Skrull. Both seek to destroy or conquer it, in order to gain tactical advantage in their war.