Nation does not mean modern political state in most of its uses - it means an ethnic group. The nation-state was for the most part basically a 19th century invention. But that's neither here nor there. Persian is related to most of the currently spoken European languages:
Persian is a member of the Indo-European family of languages, and within that family, it belongs to the Indo-Iranian (Aryan) branch. Scholars believe the Iranian sub-branch consists of the following chronological linguistic path: Old Persian (Avestan and Achaemenids Persian) ==> Middle Persian (Pahlavi, Parthian, and Sassanids Persian) ==> Modern Persian (Dari, c. 900 to present.
Old Persian, the main language of the Achaemenid inscriptions, should not be confused with the non-Indo-European Elamite language (see Behistun inscription). Over this period, the morphology of the language was simplified from the complex conjugation and declension system of Old Persian to the almost completely regularized morphology and rigid syntax of modern Persian, in a manner often described as paralleling the development of English. Additionally, many words were introduced from neighboring languages, including Aramaic and Greek in earlier times, and later Arabic and to a lesser extent Turkish. In more recent times, some Western European words have entered the language (notably from French and English.)
The language itself has greatly developed during the centuries. Due to technological developments new words and idioms are created and enter into Persian like any other language. In Iran the Academy of Persian Language and Literature is a center that evaluates the new words in order to initiate and advise its Persian equivalent. In Afghanistan, the Academy of Sciences of Afghanistan does the same for Afghan Persian (among other languages).
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The various subgroups of the Indo-European family include (in historical order of their first attestation):
* Anatolian languages — earliest attested branch, from the 18th century BC; extinct, most notable was the language of the Hittites.
* Indo-Iranian languages, descending from a common ancestor, Proto-Indo-Iranian
o Indo-Aryan, including Sanskrit, attested from the 2nd millennium BC
o Iranian languages, attested from roughy 1000 BC, including Avestan and Persian.
* Greek language — fragmentary records in Mycenaean from the 14th century BC; Homer dates to the 8th century BC. See History of the Greek language.
* Italic languages — including Latin and its descendants, the Romance languages, attested from the 1st millennium BC.
* Celtic languages — Gaulish inscriptions date as early as the 6th century BC; Old Irish texts from the 6th century AD.
* Germanic languages (including English) — earliest testimonies in runic inscriptions from around the 2nd century, earliest coherent texts in Gothic, 4th century.
* Armenian language — attested from the 5th century.
* Tocharian languages — extinct tongues of the Tocharians, extant in two dialects, attested from roughly the 6th century.
* Balto-Slavic languages, believed by many Indo-Europeanists to derive from a common proto-language later than Proto-Indo-European, while others are sceptical and think that Baltic and Slavic are no more closely related than any other two branches of Indo-European.
o Slavic languages — attested from the 9th century, earliest texts in Old Church Slavonic.
o Baltic languages — attested from the 14th century, and, for languages attested that late, they retain unusually many archaic features attributed to Proto-Indo-European.
* Albanian language — attested from the 16th century; relations with Illyrian, Dacian, or Thracian proposed.
In addition to the classical ten branches listed above, there are several extinct languages, about which very little is known:
* Illyrian languages — probably related to Messapian; relation to Albanian also proposed.
* Venetic language — close to Italic.
* Messapian — not conclusively deciphered.
* Phrygian language — language of ancient Phrygia, possibly close to Greek, Thracian, or Armenian.
* Paionian language — extinct language once spoken north of Macedon.
* Thracian language — possibly close to Dacian.
* Dacian language — possibly close to Thracian and Albanian.
* Ancient Macedonian language — probably related to Greek, others propose relation to Ilyrian, Thracian or Phrygian.
* Ligurian language — possibly not Indo-European; possibly close to or part of Celtic
There were no doubt other Indo-European languages which are now lost without a trace. The fragmentary Etruscan and Rhaetian languages cannot be classified with any certainty, although they are probably non-Indo-European.
Language tree map time. ;')
As to your assertion that "Persian is related to most of the currently spoken European languages", I could use a little help beyond a linguistic map of the ancient world that connects all languages used from Ireland in the West to India in the East. How specifically is Persian related to, let's say, Dutch? What words are in common? What verb tense patterns are common? Are adverb and adjective use structures the same?