For those of us who were there in Zimbabwe twenty years ago, it's agonising to see how quickly and steeply the country has descended into poverty, corruption and violence. In those days there was far more optimism than foreboding. The country was rich and fertile. With the Victoria Falls, Kariba and Wankie game park, it was sensationally beautiful and tourism was about to take off. Race relations could only be thought good if you lived in blinkers, but they certainly lacked the bitterness of apartheid South Africa. Even at the height of the civil war anyone, white or black, could walk round the capital - then called Salisbury - in perfect safety. Whites had hoped that the first free elections would be won by Bishop Abel Muzorewa, but he was seen as a tool of the white oppressors, and never stood a chance against Robert Mugabe. Even so, whites were prepared to give him the benefit of the doubt. After all, while he called himself a Marxist, he claimed he had learned the lesson of Mozambique, which was not to expel your white farmers.    Well, the farmers know better now. There was always something rather naive, sometimes engagingly so, about Zimbabwe's white people, the lost tribe of Africa. Some, mainly in the towns, were breathtakingly rude to their black employees ("munts" was the favoured term of disparagement), and gave the impression that they didn't even realise how humiliating they were. (Who in their right mind wants to be surrounded by people who detest you?) The farmers often believed that they were deeply loved by their workers. They pointed to the accommodation, the schools and the full dinner plates and contrasted this comparative comfort and security with the spiralling descent of Zambia,  just across the Zambezi. Even the tiny handful of white Guardian Weekly-reading liberals were horrified at that decay. The distinctly unliberal majority had a simple world-view, expressed by Ian Smith, their spiritual as well as political leader, who told me that the capture of southern Africa was a straightforward communist plot, masterminded from Moscow, permitted by gullible and feeble Europeans.     It was then, as now, a land of the most puzzling contrasts. Two decades ago I sat in a beautiful, white-owned Salisbury garden, lunching with among others, Dumiso Dabengwa, then Joshua Nkomo's chief of staff, now the home affairs minister. "Mmm," he said with relish, as he sipped from his glass, "South African wine! Delicious! So much better than this Zimbabwean muck." I who would not have let a drop of South African wine sully my lips at home could only marvel about how much I had to learn about the continent.