Caveat Emptor, for you know not what the irresistible lure of cheaper shopping will bring, is the theme of Wall Street Journal reporter Bob Ortega's fascinating In Sam We Trust, which is billed as the untold story of Sam Walton's retail creation Wal-Mart and how it "is devouring the world".

We have minor skirmishes over out-of-town developments with rows over sucking jobs and shoppers out of urban centres and environmental concerns.

However, the US is littered with the debris of a war waged and lost, with shuttered shop windows, desolate down-towns and the ugly hulks of Wal-Marts, Kmarts et al squatting on the edge of town like giant succubuses.

Now the biggest victor has crossed the Atlantic, invaded Britain and fired the first barrage in what has all the hallmarks of a vicious retailing war. Wal-Marts' buying of Asda and the ensuing round of price-cuts and PR hyperbole is just the first taste in what promises to be a bitter clash familiar to US shoppers and well documented in this excellent account of the rise and rise of a retail giant.

Britain's big chains - and the Irish companies that supply them - have much to fear because WalMart has built its empire on ruthlessly going head-to-head with competition, using its muscle to extract favourable terms from towns desperate for the low-paid jobs provided and implacable opposition to trade unions.

Founder Sam Walton's business philosophy was simple - pile 'em high and sell 'em cheap. Not a novel one as old brand names such as Sears, Woolworths and Kmart had done the same but what Walton did was to refine this to the nth degree.

He realised that small-town America was not being serviced by the traditional giants and that these hitherto ignored markets were lucrative enough to support a superstore, especially if there was no competition.

Mr Walton established a stranglehold on this retailing niche and pared expenditure to the bone. Wal-Marts were typically cavernous places built on the edge of town, usually exempt from taxes, often subsidised and with enough space to park an armada of cars.

By refining his buying and distribution techniques and relentlessly comparing Wal-Mart to its competitors and ruthlessly under-cutting prices Mr Walton built a colossus which is now the number one in the world.

As for the future, it's just a hop and skip from Holyhead to here. . .