World View: In 1970 Spanish gross domestic product was four times higher than Morocco's, while now the differential is nearly 13. This is one of the highest gaps between neighbouring states, since the average ratio along the main 189 borders of the world is 3.5.
Only 27 per cent of these exceed this average economic "step", a term used to denote the economic difference between two countries. In contrast Luxembourg, the world's richest country, has 417.2 times the gross national income per capita of its poorest state, Ethiopia.
Thus extremely rich countries do not normally have extremely poor neighbours. Where they do, their relationship usually arises from political or military tensions and is associated with acute instability involving illegal migration, drug-trafficking, mutual resentment and contempt and - potentially or increasingly - terrorism.
Ranked by gross national income measured by purchasing power parity (which controls for currency differentials) the average gap between neighbours is 2.2 rather than 3.5, according to figures for 2001, and the Spanish-Moroccan gap is 5.5.
The 10 most unequal "steps" among neighbours are between: Saudi Arabia and Yemen; South Africa and Mozambique; Namibia and Zambia; Algeria and Niger; Algeria and Mali; Hong Kong and China; Israel and Syria; Spain and Morocco; Israel and Egypt; and Argentina and Bolivia.
These figures are worth recalling on the first anniversary of the Madrid train bombings, in which 193 people were killed and 1,900 injured.
The chief suspects are all Moroccans, 22 of whom are in custody. Remarkably, the Socialist government elected following the attacks has chosen to reverse rather than continue the stern opposition of its conservative predecessor to developing closer relations with Morocco.
Instead its leader, José Luiz Rodriguez Zapatero, has opened them up and sought to address the political, cultural and economic inequalities involved. His government has tried to improve living conditions for the roughly 400,000 Moroccans in Spain and other Muslim minorities.
It has encouraged an awareness of Spain's deep historical and cultural relationship with the Arab world. Zapatero believes a dialogue of civilisations is needed if terrorism is to be headed off by democracy, tolerance and human rights.
Such themes came through the conference on terrorism organised in Madrid this week to coincide with the anniversary.
It concluded that worldwide co-operation on intelligence, democracy, education and economic aid to developing countries are the best ways to combat terrorism. Implicit or explicit criticisms of the United States's approach to the issue were widely voiced at the conference - not surprisingly in view of the dramatic break with the war in Iraq which Zapatero's victory represented last year.
Speakers such as George Soros, Javier Solana and Mary Robinson warned that a war on terrorism which violates human rights will encourage terrorism, not diminish it.
Several US experts said Guantanamo creates an "incubator effect". Kofi Annan made a strong case that "we cannot compromise on core values". He said: "Compromising human rights cannot serve the struggle against terrorism. On the contrary, it facilitates the achievement of the terrorist's objectives by provoking tension, hatred and mistrust of governments among precisely those parts of the population where he is most likely to find recruits".
These are pointed criticisms from some of the Bush administration's usual suspects, at a time when there is a new refrain from its defenders that the President was right all along.
It reminds us he does not own the notion of democratisation and that there are varying strategies to bring it about. Introducing it at the point of a gun can backfire. Lebanon is not Ukraine, however welcome the anti-Syrian movement there after Rafik Hariri's assassination, but a complex microcosm of deeper regional conflict, including huge economic "steps" of inequality between Israel and neighbouring states.
These figures show how substantially economic inequalities between Spain and Morocco have grown in barely more than one generation. There was a sharp acceleration in the differential after Spain joined the EEC in 1986, an abrupt interruption in it when the peseta was devalued in the 1990s, followed by a further sharp increase over the last five years.
This coincided with the deterioration of relations with Morocco during José Maria Aznar's second term, when he closed Spain's borders against illegal immigration, dramatised by horrifying deaths of people trying to cross the Straits of Gibraltar.
Figures for illegal migration, human trafficking, arrests of boats and the number of corpses found on southern Spanish coasts are down this year.
But they still exemplify conditions that can incubate terrorism and which need to be tackled if it is to minimised.
Clearly, the growing gap between Spain and Morocco is largely a function of European integration, which has benefited Spain by bringing it closer to the living standards of its northern neighbours through transfers and stimulated economic growth.
The Common Agricultural Policy and regional and cohesion funds had much to do with it. Instead of growing tomatoes and fruit in Morocco and exporting them to Spain, Moroccan workers came to work in Spanish fields to produce crops that are now exported to Morocco.
In a longer perspective, political and economic changes in the last 100 years altered the previous cultural "family resemblances" across the Mediterranean in rural and urban life, from modes of dress to food and ideas about honour and group solidarities.
The south of the European countries was gradually absorbed into the north, becoming "European", while the southern "Muslim" shores were increasingly peasantised and tribalised by massive migrations into the coastal cities from the interior.
Similar effects can be expected on other EU borders, especially between acceding countries and their eastern neighbours, such as Poland and Ukraine, Finland and Russia, Lithuania and Belarus, Romania and Moldova. In recognition of the potentially negative consequences and the need to develop open political and economic relations with its new periphery, the EU has announced a neighbourhood strategy to deal with them in the longer term, including through new institutions stopping short of accession.
While praiseworthy in its intentions, this is hard to reconcile with the imposition of Schengen borders closing off these neighbourhood relations.
Zapatero's policy reminds us this is very much a southern issue, too.