Ibn Taymiyyah (d.728H) - rahimahullaah - said: 
"Everything which is outside the call of Islaam and the Qur'aan, with regards to lineage, land, nationality, schools of thoughts and ways, then it is from the calls of jaahiliyyah. Indeed, even when the Muhaajirs (those Companions who migrated from Makkah to Madeenah) and the Ansaars (those Companions who aided and supported those who migrated) argued, such that one of the Muhaajirs said:"O Muhaajirs! (implying; rally to my aid)."
And one of the Ansaar said:"O Ansaar!"
Upon hearing this, the Prophet (صلى الله علیه وسلم) said:"Is it with the calls of jaahiliyyah that you call, and I am still amongst you!"
And he became very angry at that." 
And from the textual evidences pertaining to this issue is Allaah - the Most High's - saying:
"And stay in your homes and do not display yourselves, like the display of the times of jaahiliyyah (pre-lslaamic ignorance). But establish the Prayer, give the Zakaah and obey Allaah and His Messenger." [Soorah al-Ahzaab (33):33]
"When those who disbelieved placed in their hearts pride and arrogance - the pride and arrogance of jaahiliyyah - then Allaah sent down His tranquility upon His Messenger sallallaahu 'alayhi wa sallam and upon the Believers ..." [Soorah al-Fath (48):26]
The Prophet (صلى الله علیه وسلم) said:
"Whosoever leaves off obedience and separates from the Jamaa'ah and dies, he dies a death of jaahiliyyah. Whoever fights under the banner of the blind, becoming angry for 'asabiyyah (partisanship and party-spirit), or calling to 'asabiyyah, or assisting 'asabiyyah, then dies, he dies a death of jaahiliyyah." 
Also in Saheeh Muslim (8/120) the Prophet(صلى الله علیه وسلم) said:
"Indeed Allaah has revealed to me that you should have humility, and that no one should act proudly and oppressively over anyone else, nor should anyone boast over anyone else."
And there is no doubt that the call to nationalism is a call to 'asabiyyah (partisanship and party-spirit) and it is a call to becoming angry for the sake of 'asabiyyah and fighting for 'asabiyyah. And there is no doubt also, that the call to nationalism is a call to transgression, pride and arrogance, since nationalism is not a divinely-revealed way of life which prevents its people from oppression and proud-boasting. Rather it is an ideology from the time of jaahiliyyah which leads it people to boasting about it and having 'asabiyyah for it - even if they are the oppressors and the others are the oppressed! So - O noble reader - consider this and the truth will be clear to you.
And from the textual evidences connected with this is what at-Tirmidhee relates from Allaah's Messenger (صلى الله علیه وسلم) that he said:
"Let people stop boasting about their forefathers who have died, who are merely fire for the Hell-Fire; or they will certainly be more insignificant with Allaah than the beetle which roles dung with its nose. Allaah has removed from you the party-spirit of the days of jaahiliyyah and the boasting about one's forefathers. Indeed a person is either a pious Believer or a wretched sinner. All of mankind are the children of Aadam, and Aadam was created from clay." 
The Prophet (صلى الله علیه وسلم) also said:
"Indeed there is no excellence for an arab over a non-arab, nor a non-arab over an arab, nor a white person over a black one, nor a black person over a white one, except through taqwaa (piety and obedience to Allaah)." 
And this accords with Allaah - the Most High's saying:
"O mankind! We have created you from male and female and have made you into nations and tribes, that you may know one another. Indeed the most noble of you with Allaah is the one who has the most taqwaa." [Soorah al-Hujuraat (49):13]
So Allaah - the One free from all defects made clear in this noble aayah (verse) that people have been made into nations and tribes so that they may come to know each other, not that they should boast and have pride over one another. And Allaah - the Most High - considered the most noblest of them to be the one with the most piety and taqwaa. Likewise, the previously mentioned narration shows the same meaning, and guides to the fact that it is from the ways of jahiliyyah to vainly boast and to have false pride for one's forefathers and ancestry. This is what the calls of jaahiliyyah lead to, whereas Islaam is in opposition to this. Rather Islaam calls to modesty, humility, taqwaa and to having love for the sake of Allaah, and that the true and sincere Muslims are merely one of the categories of the children of Aadam 'alayhis-salaam, and that the Muslims are a single body and a single structure; each part supporting the other and each part feeling the pain that the other parts are suffering - as occurs in an authentic hadeeth (narration) from the Prophet (صلى الله علیه وسلم), that he said:
"The Believer to the Believer is like a solid building, one part supports the other." And he interlaced his fingers to demonstrate this. 
The Prophet (صلى الله علیه وسلم) also said:
"The example of the Believer in their mutual love and mercy is like the example of a body, if one part of the body feels pain, then all the body suffers in sleeplessness and fever." 
O people! I call to you in the name of Allaah. Does your nationalism call you to these noble manners of mercy and kindness to the Muslims - the arabs and the non-arabs - and of having mutual sympathy and concern for them, and feeling pain at their pain? No by Allaah! Rather it calls you to having allegiance with those who have evil character and it calls you to cultivating enmity and hatred for those who deny this false creed of nationalism. So beware, O Muslim who desires safety and salvation, and consider the reality of the affair with a fair consideration, without being prejudiced with party-spirit and desires. Only then you will see the reality as it truly is. So may Allaah guide me and you to the means of safety and salvation.And it is related by Imaam al-Bukhaaree in his Saheeh (8/137), that a young man from the Muhaajirs and a young man from the Ansaar quarreled. So the Muhaajir said:
"O Muhaajirs! (meaning: rally to my help)" And the Ansaaree said: "O Ansaar!" So the Prophet (صلى الله علیه وسلم) heard this and said: "Is it with the call of jaahiliyyah that you are calling out, and I am present amongst you!"
Even though the term Muhaajr and Ansaar are two ascriptions which are beloved to Allaah - the One free from all defects - and He has praised these two groups with a very great praise, in His - the Most High's - saying:
"And the first to embrace Islaam from the Muhaajirs and the Ansaar, and those who followed them in goodness, beliefs and actions. Allaah is well-pleased with them, and they are well-pleased with Him. He has prepared for them Gardens of Paradise, beneath which rivers flow, to live therein forever. That is the supreme achievement." [Soorah at-Tawbah (9):100]
Yet in the above incident, this ascription to the Muhaajirs and seeking the help from them, and the Ansaar and seeking the help from them, when the likes of this was considered to be from the calls of jaahiliyyah, then what about those who claim allegiance to nationalism and seek help through that and become angry for that? Will this not be more fitting to be considered one of the calls from the days of jaahiliyyah? This is a matter in which there is no doubt, and it is one of the dearest of all matters.
And this is what has been established in the authentic hadeeth (narration), from al-Haarith al-Ash'aree radi-Allaahu 'anhu, that the Prophet (صلى الله علیه وسلم) said:
"I order you with five things which Allaah ordered me with: The Jamaa'ah, hearing, obeying, hijrah (migration) and jihaad in the way of Allaah - the Mighty and Majestic. So whosoever separates from the Jamaa'ah by a hand span, throws the yoke of Islaam from his neck, unless he repents. And whosoever calls with the call of jaahiliyyah (the days of ignorance), then he is from the hoarded-heap of Hell-Fire." It was said: Even if he fasts and prays? He said: "Even if he fasts and prays. So call with the call of Allaah which Allaah gave: The Muslims, the Believers, Worshippers of Allaah." 
This hadeeth is absolutely clear with regards to rendering futile the calls to nationalism. Its callers deserve that they should be from the heap of Hell-Fire, even if they fast and they pray and claim that they are Muslims. So what a severe threat and severe warning is given here; warning every Muslim from the calls of jaahiliyyah and warning them from entering into this - even if such calls are adorned with false talks and enchanting speeches. Rather it is a deception and a blind-following which leads its people to the worst and most despicable of ends. And we ask Allaah for safety and freedom from that.
 Majmoo'ul-Fataawaa (3/456).
 Related by al-Bukhaaree (8/137).
 Related by Muslim in his Saheeh (6/21), from Abu Hurayrah radiallaahu 'anhu.
 Hasan: Related by Abu Daawood (no.5116) and at-Tirmidhee (no.4233) from Abu Hurayrah radiallaahu 'anhu. It was authenticated by Ibn Taymiyyah in Kitaabul-Iqtidaa (p.35).
 Saheeh: Related by Ahmad (5/411) and it was authenticated by Ibn Taymiyyah in Kitaabul-Iqtidaa (p.69).
 Related by al-Bukhaaree (no.481) and Muslim (no.2585) from Abu Hurayrah radiallaahu 'anhu.
 Related by al-Bukhaaree (no.6011) and Muslim (no.2586) from an-Nu'maan ibn Basheer radiallaahu 'anhu.
 Saheeh: Related by at-Tirmidhee (nos.2863) and at-Tiyaalasee (no.1161) and others. It was authenticated by Shaykh al-Albaanee in his checking to Ibn Abee 'Aasim's as-Sunnah (no.1036).