Rambam, Shulchan Aruch, the Vilna Gaon, and a Chafetz Chaim who tried making aliya at 86.
Q. Is Aliya an Halachic Obligation?
Yes, our rabbis teach us that living in Israel is not only a halacha, but is “equated with all of the other mitzvot combined” (Sifre, Dvarim 12; Tosefta Avoda Zara 5, 2)! It is cited in the classic works of halacha, for example: the Rambam (Mlachim 5, 12, “A person should always live in the Land of Israel”), the Shulchan Aruch (Even HaEzer 75, 3, “even in a city which is mostly gentiles”, as opposed to living in “a city in chutz laAretz which is mostly Jewish”; and Shulchan Aruch and Mishna Brura, Orach Chaim, 248, 4). There are so many sources, I’ll suffice to quote the Pitchei Tshuva (Even HaEzer 75, 6) who’s job is to summarize: “The Ramban learns out the mitzvah from במדבר לג, נג, “והורשתם את הארץ וישבתם בה”, and it is a mitzvah equated with the rest of the mitzvot combined… all time periods are equal to fulfill this mitzvah (even if there’s no Beit haMikdash), and this is clear from all of the poskim, rishonim and achronim“. The Sdei Chemed (v, p. 11), also known as a “summarizer”, says almost the same, word for word. The obligation is cited by the Vilna Gaon, the Chatam Sofer, R. Ya’akov Emdin, the Avnei Nezer, the Chazon Ish and tens of others, and some, like Rashi (Yvamot 64a) goes so far as to say that living in chutz laAretz is a sin. The Chafetz Chaim even attempted making aliya at the age of 86! The Or HaChaim HaKadosh (end of parshat Netzavim) says that not only is aliya an halacha, but it is more than a mitzvah, for it “includes all of the Torah”.
In addition, as we explained many times and from many different vantage points why it’s so important, for example:
it enables all of the other mitzvot (quantity)
mitzvot in chutz laAretz are just practice (quality)
there is a living and loving eternal bond between Israel and our Land, like a man and his wife.
It doubles our Judaism, from being just a religion to being also a religion and also a nation.
It enables us to reveal G-dliness and holiness in every aspect of life, where our fruit is holy, as are our rocks, army, language, days of the week, hikes, bus-drivers, etc. etc.
I can just add the words of the Gerrer Rebbe, that today, the only one of the ten tests of Avraham Avinu that remains to help us measure our dedication to G-d is: “לך לך מארצך ממולדתך ומבית אביך אל הארץ אשר אראיך”, “leave your country, your homeland and your father’s home to go to [the Promised Land]. Anyone who sees doing the will of Hashem, and being with and building the nation of Israel as important factors in life, will undoubtedly make aliya. How much more so when Am Yisrael is at war and needs all healthy boys that can fight. Those who don’t are usually proclaiming that money, convenience and other factors are more important on his/her priority list (the Maggid of the Shulchan Aruch).