In former times communities finding themselves with a greater population than their fields could feed have taken to making goods and exchanging them abroad for foodstuffs. The part which this arrangement played in the economy of the Attic Greeks and the part which that economy played in their general history in the sixth and fifth centuries B.C. is a famous example. The locus classicus in modern times is our own country. A population that at 1700 numbered about 5 millions grew to about 8 millions in 1800. The series of changes generally summed up as the Agricultural Revolution enabled English farmers to grow the extra food. By 1900, however, the 5 millions of 1700 had become over 32 millions. To sustain so many people on the island was made possible only because we exported manufactures in larger and larger amounts in return for grain and meat and textile fibres.