In 1980, soon after the Islamic Revolution (Engelab-e-Eslami), Emam Khomeini said:
"We do not worship Iran we worship Allah; for patriotism is another word for paganism. I say let this land (of Iran) burn! I say let this land (of Iran) go up in smoke, provided Islam emerges triumphant in the rest of the world!"
Sadly, however, Emam Khomeini's vision did not fit his time well nor does ours. An Islamic Umma'ath is present, however, it's level of coordination and closeness as well integration is open to question, which to my reasoning is almost negligible. I will post a purposely chosen Hadith and Ayath.
The Prophet (peace be up on him) said, "Those that have even a drop of hate within them, shall not enter paradise."
The Qur'an states: "Believers are not more than brothers to another. Thus reconcile amongst your brethren, and fear thy Lord, that thou may receive mercy." [49:10]
At present, however, the Muslim Umm'ath has distanced itself from these teachings and destined Islamic Brotherhood to hypocrisy. I believe I have said this somewhere before also. To highlight one example, the hypocrisy of Islamic brotherhood, much exported and highlighted by the Arab states during the 70s & 80s, came alive during their united support of Saddam Yazid against a battle-weary and under-armed Muslim youth of a lone Iran whom they proudly helped Saddam bleed for 8 consecutive years. If more of this is to continue under the name of brotherhood, then I would surely salute it from a distance.
I use the above example to point out the mockery that was made out of the broader feeling of Muslim unity and solidarity during the course of the Iran-Iraq war by some of those same faces that had been outspoken in that regard. They say the tree rots from the top and this was more than evident during that period for those that worked as accomplices in imposing war on Iran.
Brotherhood requires oneness without distinction and unity in face of division to be true.
Edit:
Addressing nationalism limited to countries: At a higher level and more contemplative level, I feel ultra-nationalism can be counter-productive and lays the seeds for negativity. It forges negative views of external races, religions and cultures. In their extremity, such movements always become "purists" in the long-run and bring retrogression eventually. As William Blum put it: "If love is blind, patriotism has lost all five senses." Hence, the above quotation I posted from Emam Khomeini. He was referring to such sentiment. Love for one's own should not come from the loathing of others. In fact, Emam Khomeini asked the people to set aside their individualistic (and often individual-materialistic) urges aside in face of greater communal (national) good for all their people (and the Muslim world in a broader sense). Thought someone would need a clarification for the quote..