But inside, some of these traditional foes were warming to each other.
Smaller countries at the summit are increasingly working with protest groups to get a fair shake from the world's global trade giants - much the way black South Africans looked to international activists to help overthrow apartheid. This week, the Group of 21 developing nations, which includes China, Brazil, and India, announced an alliance with Oxfam, an international humanitarian organiza- tion based in Oxford, England. The alliance was billed as a bid to unite antiglobalization opponents with developing nations.
As well, from Latin America to Africa, poor countries are banding together, forging new accords and larger trade blocs in an effort to maximize their negotiating leverage. It marks a profound shift from the days of every man for himself - with the advantage usually going to the big guys.
"What Africa has done to a much greater extent than ever before is it's gotten its act together and done as much research and consulting as humanly possible," says Steven Gruzd, a researcher at the South African Institute of International Affairs in Johannesburg. "On an organizational level, there is much more appreciation of how serious the implications of trade are and what is at stake. And there is a coming together and sharing of ideas."
While their goals may be different - "globophobes" want to end unchecked development while smaller countries want freer access to markets for their goods - the growing unity represents a recognition that neither side can get what it wants by going it alone.
At the top of the developing world's agenda at Cancún is the elimination of tariffs and agricultural subsidies in America and Europe. Small nations say that government payments to Western farmers artificially drive down prices, preventing small farmers from competing in global markets. The US and Europe subsidize their farmers to the tune of $45 billion. Western trade representatives say they are being unfairly targeted, noting that countries like China have tariffs more than three times as high as those of the US.
Earlier this month, South African President Thabo Mbeki surprised the world when he suggested that antiglobalization protesters might be an important ally. "They may act in ways that you and I would not like - breaking windows in the street and this and that - but the message they are communicating relates to us," Mr. Mbeki told a seminar in Malaysia during a visit earlier this month. "We need to link up with our constituency in the developed world," he added, referring to antiglobalization protesters living in the West.
Celine Charveriat, spokesperson for Oxfam, says that its alliance with the Group of 21 was the best way it saw to pressure the West for fairer treatment of the world's small farmers.
"We decided to support their proposal because they want to challenge the status quo imposed by the two big subsidy superpowers - the EU and the US...." says Ms. Charveriat. "What we hope is that this can unlock the political situation here in Cancún and that it will start serious negotiations on agriculture."
Observers say that although small countries and antiglobalization groups share some of the same agendas, building lasting bridges may prove difficult. When African trade ministers met last month on the Indian Ocean island of Mauritius in preparation for this week's WTO summit, their final communiqué, intended to be a blueprint for Africa's position at the talks, was vague on important issues and criticized by nongovernmental organizations (NGOs). It fell short of making a broad condemnation of agricultural subsidies, such as the $4 billion that the US pays its cotton farmers, that NGOs say harm small farmers.
In South Africa, groups that consider themselves part of the antiglobalization movement - some of which are participating in protests in Cancún - are skeptical of Mbeki's new friendliness. They see themselves at odds with the government over issues like the privatization of services, which they say limits poor people's access to commodities like water and electricity.
"It's becoming increasingly impossible to ignore that global social movements are in conflict with the new [developing-world] liberals," says Mike Abrahams, a member of Alternative Information and Development Center, a South African NGO based in Cape Town, which sent five people to Mexico. "I think [Mbeki] hopes that there is a strong antiglobalization protest that can serve the interests of their negotiations."
Poor countries are doing their best to come to the 148-nation talks with a unified agenda. In Africa, there have been at least 15 meetings over the past two years to develop a common platform. And in Latin America, Mercosur, the world's third-largest trade bloc, just added Peru as an associate member to join founding members Brazil, Argentina, Uruguay, and Paraguay, and associates Bolivia and Chile.
But despite this new era of cooperation, some analysts predict that the developed world will stick with the divide-and-conquer strategy that has been so effective in the past. Ultimately, developing-world unity may fall victim once again to individual interests.
"I think they'll talk the talk. I think they'll probably make a big attempt to stick together," says Mr. Gruzd. "But you have to remember that trade is about interests and it's about money coming into your country."
• Andrew Downie in Rio de Janeiro and Teresa Méndez in Boston contributed to this report.