What would you say were the advantages and disadvantages of nationalism?

Here are some pros and cons of nationalism: 

Pros: 
Nationalism is the voice of the people against the autocratic monarchs. 
Nationalism is based on self determination. 
Nationalism is a unifying force with overpowers tribal identities and created a new and much more rational identity. 
Nationalism created a big government which could look after health and education of the people and be keeping the people safe. 

Cons: 
Nationalism can lead to jingoism which can include browbeatings and considering oneself superior to others. 
Nationalism can lead to world wars and nuclear weapons. 
Nationalism can lead to isolation of a society and from other countries. 

I hope this helps you!