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

Yours is understandable, but this sounds more natural.

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

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

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

Scientists were carefully with the hazardous chemicals of the bomb. Scientists were careful with the hazardous chemicals of the bomb.

Scientists were carefully with the hazardous chemicals ofin the bomb. Scientists were careful with the hazardous chemicals in the bomb.

Or 'were carefully working with...'

Scientists were carefully with the hazardous chemicals of the bomb. Scientists were careful with the hazardous chemicals of the bomb.

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

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

AnywayHowever, there wasere a lot of incidents in the atomic experiments. However, there were 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 war. For some people, the atomic bomb is one of the most evil things created by humanity, but others think this is a necessary evil to stop the war.

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

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

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