"Eye for eye and tooth for tooth has gone too long in the world"

This old age adage has been practicing since early ages. Motive behind this was to punish culprits and to provide justice and relief to innocents.
It was believed that capital punishment would serve as deterrent but later it was realized that it was not giving desired results. Crimes were not decreasing despite they were increasing at greater pace, not only this but also it was leaving detrimental effects on the society.
If we glance through history we will find myriad of examples. In World War-I Germany fought with allied powers and faced shameful defeat. What allied powers did with Germany? they mistreated her, ruined her economy as she could not rise again. It inculcated sense of revenge into the minds of Germans, which ultimately resulted in World War-II in which millions of people died. What would have happened if the Allied powers had treated Germans well, world could have been saved from catastrophic destruction of World War-II.
Butchering of innocent Palestinians by Israel is also one the example of this. More than two thousand Palestinians have been killed in the revenge of assassination of three Israelis. If Israelis would have taken those culprits instead of killing thousands of Palestinians that would have been much better.
Though forgiveness is better than revenge, but at some places and situations it becomes the need of hour to punish criminals, for whom crime is nothing but a mere amusement and killing humanity is nothing but a profession.

Flaw#1
First sentence needs correction and should've come after first sentence which usually deciphers the meaning of the saying.It will be "The reality that this old adage signifies has been practised".
We can't practice maxim.Instead,People tend to do what it emphasizes.

Flaw#2
You also misinterpreted the meaning of the maxim.It says that taking revenge proves disastrous.In other words,if there is tension between two communities and both of them reciprocate violence then the world will ultimately suffer.At least one group must adopt patience so that survival could continue.

Flaw#3
The second paragragh had been written in past tense.Remember use past tense for situations which no longer exists.On the other hand,Capital punishment is still believed to be an effect tool to combat militancy.

Flaw#4
In 3rd Paragraph,You wrote about the abandoning of Germany's Allies which is totall off topic.And also prefer 3rd person to 1st or 2nd person such as 'we'.

Flaw#5
You had better structured the palestinian example as,"More than two thousand innocent civilians have been killed as a result of Israel's revenge for its 3 soldiers assassination".

Overall you attempted good.Not major mistakes.These will ultimately improve if you practice on daily basis.

Good Luck.

"Conscience is the basis for Justice"

Conscience is a person's awareness of right or wrong with regard to his/her own thoughts and actions. What you want to do with others same could happen to you, in this regard, you treat others in a way you wanted to be treated this forms the basis of justice.
Taking ordinary example to explore this concept, a rich man should treat a poor in a manner he wanted to be treated if he were poor. Similarly, a businessman should produce or sell commodities of same quality which he wants for himself. This ultimately leads towards just behavior.
Powerful nations should also think same as the are thinking for themselves. There should not be double standard in their policies. As for America, she is against the monarchy and wants to abolish Assad's regime in Syria on the other hand it is supporting monarchy in Saudi Arabia which is against the moral obligations.
Though conscience is inner sense which aware us what is right and what is wrong but the perception of right and wrong varies from persons to persons. As for Taliban, fighting people, killing them brutally are pious acts, but for others these are terrorist acts. Therefore it is necessary that conscience should be assumed generally as fair.