A lot ofMany years ago, the atomic bomb was created.

Scientists were carefully with the hazardous chemicals of the bomb.

For some people, the atomic bomb is one of the most evil things created by the humanity, but others think this iwas a necessary evil to stop the war.

A lot ofMany years ago, the atomic bomb was created.

'Many years ago' is a very common phrase - it might be good to remember!

Scientists were carefully with the hazardous chemicals ofin the bomb.

Or 'were carefully working with...'

AnywayHowever, there wasere a lot of incidents in the atomic experiments.

Instead of 'Anyway', using 'However' works better. The previous sentence implies that the scientists were careful --> so you would think there are no accidents. But in the next sentence, you introduce the contrary idea: even though the scientists were careful, there were accidents. To show these contrasting ideas, using 'However' is better.

For some people, the atomic bomb is one of the most evil things created by the humanity, but others think this is a necessary evil to stop the wars.

Or 'is the most evil thing created by...' | If using 'the war' tell us what war it is!

A lot ofMany years ago, the atomic bomb was created.

Yours is understandable, but this sounds more natural.

Scientists were carefully with the hazardous chemicals of the bomb.

Anyway, there wasere a lot of incidents in the atomic experiments.

'was' is for one singular thing, 'were' is for multiple

For some people, the atomic bomb is one of the most evil things created by the humanity, but others think this is a necessary evil to stop the war.