This is a classic example of strategic management. A series of factors in the macro environment increase the attaractiveness of an industry. BHP enters this industry, with an aquicition (note the bidding process). This is a vertical integration. Their strategy is justified by their long the vision.
BHP Billiton launches hostile bid for Potash
Mining giant BHP Billiton has launched a $40bn (£25.8bn) hostile takeover bid of Canadian firm Potash Corp after having had an initial offer rejected.
On Tuesday, Potash, the world's largest fertiliser producer snubbed BHP's offer, saying it undervalued the firm.
Read the whole article at: http://www.bbc.co.uk/news/business-11009145