I partially agree but i do not believe that even the greatest leaders can make the people change their values or genetic predispositions. There has to be the right medium for any ideas to grow. I do not think all americans will now change and become sexist racist opportunists like Trump. Aslo , there are still bad people in Poland just like anywere else in the world but just not so many ..thats why they could not take over.Yes I can relate to your country history and other countries. France and Great Britain has a war for 100 years but are friends and civilized people. Spain and Germany both wreaked havoc on Europe for a period of time in different times of history yet now they are friendly wit all Europe.
First you should understand that for example your people in Poland didn't for a sudden became friendly by themselves! If you left to the people I can assure you there will still be hatred and even wars! But all thanks go to the leaders, the thinkers and rational people in command who saw it's better to overcome the hatred and be friendly and install great values in the Polish people! Your leaders work so hard on this, they were not greedy and selfish, and did their best to create a great version of a Polish citizen.
In Tunisia, or any other 3rd world country, people went through many hardships and experiences in their history, they built bad habits and ideas and mindset. There came leaders, who wanted to change, but first their were limited in number unlike Europe, and they were not that driven. Some were selfish, some were a bit lazy, some didn't find all the means to change, etc... So the outcome wasn't a great version of a Tunisian or a Moroccan that can be compared to the Polish or German version.
Always remember that 5% always lead the rest. So if the 5% isn't that great the rest won't be that great too!