Love of one's homeland, and nationalism/patriotism are somewhat different things.
Love of Allah's creation is a good thing, and it is also a good thing to want to care for and defend your homeland.
Nationalism and patriotism in the modern era are ideological movements. Nationalism oftentimes relates to an arbitrarily drawn set of boundaries which separated formerly related peoples.
Today, nationalism and patriotism have an ugly side which can sometimes lead to hatred of the "other" or the "outsider", worshipping the flag, or caring only about what happens to the people within one's nation-state or ethnic/racial group. (For instance, neo-nazism.)
So it is good to love and develop one's homeland, but it is also good to be cautious about the negative side of modern nationalism.
Regarding hadith, there is a narration that love of one's homeland is part of faith (hubb al-watan min al-iman). However, the narration is weak, and poorly sourced, and some people consider it to have been fabricated so it is not really certain that the Prophet (S) said it, although it is often quoted today. Watan (homeland) here has also been understood to mean the hereafter, since the hereafter is the final home of everyone.
Here are some reflections by 'Allamah Tabataba'i in Tafsir al-Mizan on the nature of a society which might be pertinent. As one can see, a society is inherently neither good or bad (thus, supporting it is not inherently good or bad in and of itself, and most societies have both good and bad):
"The Qurʾan teaches that society is formed from a collection of individuals while being more than merely the sum of its parts. When people form a society, they create a new entity with its own life and identity. A society lives, ages, and dies; feels and decides: grows weaker and stronger; has its own duties; and is capable of both virtue and wickedness, and of attaining both happiness and misery, just like any individual human being. All of this has been explained by a multitude of verses in the Qurʾan, and it is something we have repeatedly pointed to through the course of our previous discussions."
