Even prior to the modern era, Jewish people had settled all across Europe, the Middle East, North Africa, the Horn of Africa, and small Jewish communities could be found in places as far-flung as China, India, and Southern Africa. Indeed, Jews were among the first Old-World nationalities to settle in North America. Still, there are certain key events and migrations that should inform your project.
The year 1 - The good Diaspora: At the start of the study period, Jewish communities populated by people taking advantage of freedom of movement and security n the Roman and Parthian (Persian/Iranian) Empires, existed all over the Roman and Persian/Iranian world, Still, in CE 1 the center of Jewish culture was their ancestral homeland of Judea. If your ancestors were Iraqi or Iranian Jews in CE 1800, their ancestors probably lived in those same regions in CE 1 as participants in the "good diaspora."
First and Second Centuries - The bad Diaspora: Two revolts in the first and second centuries deprived the Jews of their cultural center. Refugees went not only to Roman and Iranian lands, but to Arabia (particularly Yemen) and Ethiopia. If your ancestors are Ethiopian, or Yemeni Jews, their ancestors were probably both there and in Judea in CE 1. Remember, at this time, laws charting Jewish heritage through the mother were new and weakly enforced. Many Jews married locals in their new homes. Don't assume that all of your ancestors from this period were Jewish. Also note: Most of the Jews who remained in Judea after the second (Bar Kochba) revolt gradually lost their Jewish identity, especially after Judea became part of the Muslim Umma. If your ancestors were Palestinian Jews in 1900, their ancestors had probably immigrated back from some other region sometime during the previous 500 years.
Seventh Century: the Khazar kingdom. During the seventh century, an interesting nationality from Western Siberia (just east of the Urals), the Khazars settled in the southern Ukraine, where they controlled the trade coming down the major rivers of the Black Sea. The Khazars ruled a multiethnic/religious knigdom, but their ruling class is noted for having converted en masse to Judaism. By the eleventh century, they had vanished as a nation (although their genes presumably live on among people of the region). The debate still rages as to whether the Ashkenazi Jews of Eastern Europe are in any part descended from them. Standard history suggests that the Ashkenazim didn't make it to Eastern Europe from their German homeland until the thirteenth century, long ater the Khazars vanished as a nation, but who knows. If you are buy the idea that the Khazars assimilated with Ashkenazi Jews, and your ancestors were Jews living in the Ukraine in 1490 CE, you may assume that they had Khazar-Jewish ancestors in Southern Ukraine in CE 1000 and Western Siberian ancestors in 1 CE. (Incidentally, if you want to see some very irrational rants on all sides, do a web search for the word "Khazar.")
711 CE - Judeo-Islamic Iberia: For some reason, the Catholic Church of Spain was particularly hostile to Jews. During the Visigothic kingdom of Spain, Jewish fortunes rose and fell depending on the benevolence of whoever happened to be in charge. The Muslim Umma quickly absorbed most of Iberia after Tariq ibn Ziyad's daring conquest in 711. Tariq's army was very small, so when the Muslims sought to augment their occupation force by calling for volunteers to help hold their new possessions, the Jews stepped forward. Consequently, in Islamic Spain, Jews enjoyed their greatest freedom and privilege between the destruction of the Temple and the Enlightenment and occupied high posts in Muslim governments. God knows exactly how cozy that relationship got, but if your ancestors lived in Iberia in 1000 CE and were Jewish, then their ancestors possibly also lived in North Africa and the Arabian Peninsula in 1 CE. (See Iberia for more)
Thirteenth Century - Crusaders and Ashkenazim: The Rhine valley had been the home to large Jewish communities since the Roman era. During the excitement of the first crusade, many armies formed and departed for the Middle East. Some were professional while others were illiterate disorganized mobs. The latter had a habit of attacking the "infidel" at home before heading for the Middle East, and German Jews suffered great violence. At this time, the Jews began to move east into Slavic and Baltic countries, taking their Medieval German with them, the basis of the Yiddish language. If your ancestors were Eastern European Jews in 1490, their ancestors probably lived in Western Germany in CE 1000.
1492 - The Sephardic Jews: When Ferdinand and Isabela conquered Granada, the last Islamic city in Spain, the first item on their agenda was ordering the conversion or expulsion of the former Muslim ruling elite and their Jewish fellow-travelers. Spanish Jews immigrated en masse to Portugal (which expelled them in turn a few years later) North Africa, and the Ottoman Empire. Like German Jews two centuries earlier, they took their language with them, so Renaissance Spanish became the basis of the Ladino language spoken in the Balkans and Middle East. If your ancestors were Jews living in the Balkans, Anatolia, North Africa, and Palestine in CE 1800, their ancestors very likely lived in Spain in 1490. Note: the Jews who left Portugal mostly ended up in the Netherlands. Many of these eventually turned up in Dutch colonies in the New World, particularly New Amsterdam (Later New York). If your ancestors were Dutch or New York Jews in CE 1800, there's a very good chance that their ancestors were in Spain and Portugal in CE 1490. Many Spanish Jews either converted to Christianity (St. Catherine of Avila and Tomas de Torquemada were both of Jewish ancestry) or went underground, passing themselves off as Christians. If your family is Hispanic but has folklore of Jewish ancestry or preserves Jewish folkways (such observance of kosher laws) then you probably had Jewish ancestors in Spain in 1490.
1600s - Ashkenazim move East: The combined kingdoms of Poland and Lithuania take over the Western Ukraine. Rather than administer their new lands in person, Polish nobles employ Jewish overseers to do so. This is the origin of heavy Jewish settlement in the Ukraine. (And of Ukrainian resentment of Jews whom they saw both as infidels and as the agents of a foreign power.) If your ancestors were Ukrainian Jews in CE 1800, their ancestors probably lived in Poland and Lithuania in CE 1490. But remember, if you have Khazar ancestors at all, you would have picked them up here.
From this point on, look to your family history for illumination.