Among the EU partners are coutries that had been at war with each other, coutries that have had colonies and others not, countries that have different principal religions, countries that don't have ID cards while others do, coutries that dispise monarchies and others that live confortably with them.
In short: there is a huge diversity, not only in our various pasts but also in our languages, our temperaments. In Belgium, patriotism is practically non-existant, while it still is very present in France, much less in Germany where regions matter more than the country.
If there are important issues, there will be a common agreement on how to react towards them.
If I remember well, Palestine was under UK protectorate and it was left to the jews after they forced their way with (among other things)terrorist attacks towards the locals and the Brits. This was years before the EU was even created.
Now, Israel only wants the US mediation and will ignore any initiative coming either from the EU or from individual European countries.
I'm not at all convinced that countries hate others. After all, it's in everyone's interest to trade with each other, to exchange goods, energy sources, cultural products, etc...So, maintaining trade keeps war away and mutual trust closer. Some tyrant might very well hate another country, granted. But I'm not sure that he can have the power to hurt it, unless he can show his countrymen how that other country answers to his provocation. Words are sometimes far more powerful than weapons. Words are the only way to establish peace.

Raoul