Defensive index? (Kebir Blue)

I'm new to this game. What's the most effective way to raise my defensive index?

Missile interceptor batteries. YOu need about 230 of them to increase the index by 1%.

Thankyou. Does it also help to join a federation, or does that make any difference?

It helps. People from a fed will help you to learn the game and protect you if you join the right one. My advice - do your research before you join one.

To be clear tho... Joining a fed has no direct impact on your indexes. It does not give any defensive index points. It helps to protect you in a real war of course, and also helps you learn the game, but numerically, it does not enter the calculation of indexes.

Thank you, both.