Shall I use "without doubt" or "without a doubt" to start my sentence in an essay?

Without a doubt is the more common/grammatically correct term

Both work, but the expression "without a doubt” is generally employed more frequently ...

Explanation:

Alternatively:

certainly, doubtless, assuredly, beyond (a) doubt, etc.

life will not be easy it will be filled with war, lack of resources, damaged planet, and lack of land to live on.

i imagine life will be easier in the sense that we will have better technology and better health and medical advances as well as infustructure growth and economic resilliance we will have much stronger militaries and probably be constintly fighting with other countries for resources and lang that is actually cleanenough to live or farm on . as well i think the need for fresh water will only brainliest answer lol

the eye wink at the hand; yet let that be / which the eye fears, when it is done, to see.