What does Islam say about enemies?

You are right "Fallen" that satan is an enemy as stated by Qura'an. But Qura'an also does mention id satan was a jinn or angel. We need to know what he was rather than speculations, Here's what Holy Qura'n - the word of Allah ta'ala says  ;

Allah points out to the Children of Adam the enmity of Iblis towards them and their father before them, and rebukes those who follow him and go against their Creator and Master. It is He who created them from nothing and sustains and nourishes them by His kindness, yet they still took Iblis as their friend and declared their enmity towards Allah. So Allah says:

(And (remember) when We said to the angels), meaning all the angels, as was mentioned in the beginning of Surat Al-Baqara

(Prostrate yourselves unto Adam) a prostration of respect and honour, as Allah says:

(And (remember) when your Lord said to the angels, "I am going to create a human (Adam) from dried (sounding) clay of altered mud. So, when I have fashioned him completely and breathed into him the soul which I created for him, then fall (you) down prostrating yourselves unto him.) ﴿15:28-29

(So they prostrated themselves except Iblis. He was one of the Jinn;) meaning, his original nature betrayed him. He had been created from smokeless fire, whereas the angels had been created from light, as is stated in Sahih Muslim where it is reported that `A'ishah, may Allah be pleased with her, said that the Messenger sallal lahu alaihi wasallam

(The angels were created from light, Iblis was created from smokeless fire, and Adam was created from that which has been described to you.) When matters are crucial, every vessel leaks that which it contains and is betrayed by its true nature. Iblis used to do what the angels did and resembled them in their devotion and worship, so he was included when they were addressed, but he disobeyed and went against what he was told to do. So Allah points out here that he was one of the Jinn, i.e., he was created from fire, as He says elsewhere:

(I am better than he. You created me from fire, and You created him from clay.)﴿38:76﴾ Al-Hasan Al-Basri said, "Iblis was not one of the angels, not even for a second. He was the origin of the Jinn just as Adam, upon him be peace, was the origin of mankind.'' This was narrated by Ibn Jarir with a Sahih chain.

(he disobeyed the command of his Lord. ) meaning by stepping beyond the bounds of obedience to Allah. Fisq (disobeying) implies going out or stepping beyond. When the date emerges from its flower, the verb used in Arabic is Fasaqat; the same verb is used to describe a mouse coming out of its hole when it comes out to do damage. Then Allah says, rebuking those who follow and obey Iblis:

(Will you then take him and his offspring as protectors and helpers rather than Me) meaning, instead of Me.

Hope this info sourcing from tafsir Ibn Kathir will clear us if satan was a jinn or angel.

Assalamu'Alaikum,

Insha'Allah before you can make a decision of who you should claim as your enemy perhaps it would be best to review who you should claim as a friend...

"Allah does not forbid you from those who do not fight you in the matters of your religion and those who did not expel you from your homes, that you show them courtesy and kindness and act justly with them because Allah loves those who are Just."(Al-Mumtahanah: 8)

So those who respect your religion and human rights, then you should deal with them in kindness and courtesy and have good dealings with them especially in matters of human welfare and well-being.

Allah says, "Co-operate with each other in matters of righteousness and piety and do not co-operate in matters of aggression and sin." (Al-Ma�idah: 2)

When you are with them (non-Muslims) it does not mean you forget your religion. So when it is time to pray you must pray. When eating with them be sure to observe the Halal. If there is a mixed gathering of males and females, remember to observe the Islamic manners of how to act in such instances. Remember that Islam commands good behavior and good dealings with all people."

MasSalaama