You don't have the defend the topic you can easily frame a thesis statement against it. Also your friend is right; this topic isn't micro but of a macro level. You aren't supposed to write from Pakistani or European or American perspective but instead point out whether nationalism is what is essentially stopping world peace. I think to an extent it is. (So beyound this are a few arguments in favour of the statement). We all care for "our" group or people first. Everyone else is "other". This concept is not bad. It helps maintain stability in society and nations. Nationalism unites us basically. But it has also been the cause of conflicts and wars. Let me give an example of Israel; they have a strong sense of nationalism (the correct term is Zionism) and it stands in the way of them feeling any sort of empathy or sympathy for the Palestinians and hence justifying all sorts of crimes in order to "protect" their claimed homeland. Another example is the rise of American nationalism (Trump and the Make America great again campaign) which has made them blind to the plight of refugees and immigrants. They have lost empathy.
Here is an article which outlines the statements made last year by U.N. High Commissioner for Human Rights Zeid Ra’ad Al Hussein warning that the rise of extreme nationalism is threatening global peace and security.
https://www.google.com/url?sa=t&sour...iP4A_W&cf=1