Introduction
The Book of Isaiah like all of Scripture is directed primarily to the nation of Israel. Israel as a nation is divided into two sections: Judah, i.e. the Jews, and Joseph meaning the Lost Ten Tribes. 
We have divided our Summary of Isaiah into two sections:
(a) Highlights of Brit-Am from the point of view of the Lost Ten Tribes.
(b) A general summarization of Isaiah by chapters.
 
ISAIAH: Brit-Am Highlights
 
            Isaiah spoke of the division between Israel (The Lost Ten Tribes) and Judah (7:17-18) (8:8). In Isaiah 7:17 the division is referred to as the worst calamity that ever overcame the Children of Israel. Isaiah also recalls situations in which the various sections of Israel will be opposed to each other:
[Isaiah 9:21] MANASSEH EPHRAIM, AND EPHRAIM MANASSEH, AND TOGETHER THEY ARE AGAINST JUDAH. FOR ALL THIS HIS ANGER IS NOT TURNED AWAY AND HIS HAND IS STRETCHED OUT STILL.
Isaiah predicted that in the Last days only a few would survive and that disasters would occur: 
[Isaiah 10:22] FOR THOUGH YOUR PEOPLE ISRAEL BE AS THE SAND OF THE SEA, ONLY A REMNANT OF THEM WILL RETURN. DESTRUCTION IS DECREED, OVERFLOWING WITH RIGHTEOUSNESS.
BE AS THE SAND OF THE SEA: Descendants of Israel will be exceedingly numerous towards the end times.
DESTRUCTION: A great calamity may take place. Only a few may survive. Likewise, Zechariah (13:6-9) indicates that two-thirds of the people will perish. The remnant will be saved and reconciled with God. The exiles of Israel who were taken to Assyria, Egypt, Pathros, Cush, Elam, Shinar, Hamath, and the Isles of the Sea (and from there moved to other regions) will return (Isaiah 11:11).
Isaiah foresaw the re-unification and ingathering of THE OUTCASTS OF ISRAEL, AND GATHER THE DISPERSED OF JUDAH FROM THE FOUR CORNERS OF THE EARTH (11:12). The northern Tribes were cast out to specific regions and stayed together whereas the Jews of Judah were dispersed all over the world.
There will be an end to anti-Semitism on the part of Ephraim and fiction with Judah:
[Isaiah 11:13] THE JEALOUSY OF EPHRAIM SHALL DEPART, AND THOSE WHO HARASS JUDAH SHALL BE CUT OFF; EPHRAIM SHALL NOT BE JEALOUS OF JUDAH, AND JUDAH SHALL NOT HARASS EPHRAIM.
THEY [i.e. Judah and Ephraim together, see verse 11:13] WILL CAUSE THE PALESTINIANS TO BE FLOWN AWAY TO THE WEST (11:14 Isaiah). Judah and Ephraim together will plunder the peoples of the east, defeat and subdue certain European nations such as Edom, Moab, and Ammon (11:14). The Return will be accompanied by great miracles (11:15).
Isaiah prophesied before and during the exile of the House of Israel. He described the exile of the northern tribes and the land of Israel being completely emptied out (24:3). The exiles would be taken to the west (24:14) where they are exhorted to glorify God from the fires in the Isles of the Sea (24:15) meaning in the Isles of Britain:
Isaiah says that the nation will be increased greatly and be removed unto the ends of the earth (24:16, 26:15) meaning the geographical extremities of the world such as Britain, North America, Scandinavia, Western Europe, Australia, New Zealand and South Africa. Those who had been exiled by the Assyrians and were lost together with those (of Judah) taken captive to Egypt will return with the blowing of a great shofar. The returnees will worship God in the Holy Temple Mount in Jerusalem. (27:13). Isaiah described the drunkards of Ephraim (28:1). The Lost Tribes will not be familiar with Hebrew and will speak with another tongue (28:11). They will be in islands (41:1), in the best places (translated in the KJ as chief men), at the ends of the earth (41:8-9). The Lost Ten Tribes (42:6) in the islands will become A COVENANT OF THE PEOPLE in Hebrew a Brit-Am. They will be a Light to the Gentiles meaning a civilizing influence. From the end of the earth and the isles they will be sea-goers (42:10). The enemies of Israel, including those of the Lost Ten Tribes, in their places of Exile are the enemies of God Almighty (42:13). The exiles are fulfilling the purpose of God in this world and even though they do not recognize it and are blind to it they are also His servants and HIS messenger (Isaiah 42:19).
            Egypt shall be subjected to Israel. Cush (translated as Ethiopia but also applicable according to the Aramaic translation and related tradition to India and its neighborhood. Black Africa (Seba) will be yours.
            Isaiah (43:3) predicted that Cush (India) and Seba (Black Africa) would be subjected to Israel. Isaiah (44:28) mentioned the name of Cyrus even though he prophesied close to 200 years before his time. The Prophecies of Isaiah concerning Cyrus on the whole refer to the Lost Tribes as we have explained. Whatever passes via (Hebrew yigia translated as labor but really meaning come unto) Egypt, and the merchandise of Cush (India not Ethiopia as translated in the King James), shall be yours and the tall Sabaean African Negroes will pass over unto you in chains (Isaiah 45:14). In the end they will acknowledge that God is with you. There is no other. Isaiah (43:3 and 45:14 and the verses around them). Isaiah (43:5-6) said that the exiles would be ingathered from the east and west, north, and south, and from the ends of the earth. Only the English-speaking nations have fulfilled these prophecies as they were written. Only they received the Promises.
Isaiah  speaks of the Isles (49:1), of raising up the Tribes of Jacob (49:6), and of the preserved of Israel who will be a light unto the Gentiles and bring salvation unto the end of the earth. The flag of Britain is called the UNION JACK (i.e. union or covenant of Jacob) and the nickname YANKEE for North American derives from a form of the name Jacob.
In an aside Isaiah refers to the Jews of Judah (49:7) who were despised in their places of exile. In the last days princes will give them honor and bow down to them because no matter what they did remain essentially faithful to the God of Israel.
Isaiah says (49:8) that the exiled of Israel will be preserved and become a covenant of people (in Hebrew a Brit-Am), who will establish the world and inherit wasted heritages. They will use released prisoners to colonize these heritages (49:9), as the British did at first in North America and Australia. They shall return from the north and from the west, and from the land of Sinim. The Land of Sinim is rendered as Australia.
            Isaiah (49:13) again turns to Judah who feels forgotten (49:14). God will return and comfort Judah and recompense him for all the troubles that passed over them and greatly increase his population (49:18-20). When Judah sees the Lost Ten Tribes returning (49:21) he will ask, Where did these come from? I was alone and persecuted, and driven from country to country.  Isaiah returns to speak of the comforting of Judah and says that those who oppressed the Jews had in effect denied the existence of the LORD God of Israel (49:26). The Isles shall wait for the salvation of God (51:5). The non-Israelite Gentiles shall no longer be allowed to occupy and degrade Jerusalem (52:1) as the Arabs now do. Isaiah predicts that a future Messiah, descendant of David (55:3-4), will come and deliver Israel. Whatever has been prophesied will come to pass (55:11).
            The descendants of non-Israelites who attach themselves with Israel will receive an inheritance alongside their fellow Israelites (55:6). The ingathering will be in stages (56:8). A redeemer (59:20) will come to Zion (the Jews) and to those who turn away from sin in Jacob, i.e. The Ten Tribes.

Isaiah foresaw reconciliation between Judah and the Lost Ten Tribes. The Lost Ten Tribes would be in areas where the British and North Americans and their kin now are. They would do things that these people did do. They are the only ones who fit the description.
 
 

chs. 1 to 10 Summarised

See also:
Brit-Am Commentary to the Book of ISAIAH
Biblical Proofs
http://www.britam.org/Proof/ProofsIntro.html