This week, Cyril Ramaphosa addressed the United Nations General Assembly in New York for the first time as president of South Africa. He spoke about the legacy of Madiba, Security Council reforms and Africa's priorities. On the same day, United States President Donald Trump made clear his intentions to cut off foreign aid to countries who don't respect the US. John Stremlau, visiting professor of International Relations at Wits University and former vice president for peace programmes at The Carter Centre, gave his impressions of Ramaphosa's and Trump's appearances.What did you think of Ramaphosa's maiden address to the UN General Assembly and how he presented the African (and South African) agenda?Ramaphosa did extremely well and presented a good argument for South Africa's world view, in contrast to the self-aggrandisement and "America first" speech Trump made. He covered a number of things on the African long-term agenda, such as getting more representation of African views in the UN. He also put down a marker on UN Security Council reform, although I don't think that is realistic in the foreseeable future.By wrapping himself in the Mandela legacy, Ramaphosa reminded the world of what is possible and the world rose to that by virtue of the way the statue of Mandela was unveiled. This, and the positive things UN Secretary General António Guterres said about Mandela, was the total opposite of the really terrible speech that Trump gave.Ramaphosa emphasised that Africa's population is increasingly becoming younger. This is something that British Prime Minister Theresa May also mentioned when she was in South Africa earlier this year. Why is this so important? It's such an important issue and I'm very glad it was mentioned. I do, however, have to caution that the temptation to see it as a positive is overshadowed by the enormous risk and cost to the population explosion in Africa.It is astounding that the sub-Saharan proportion of world births has gone from 16% to 27%, and it's going to be 37% by 2050. This places serious constraints on development. We have a huge challenge in this regard in South Africa, but at least the birth rate here is at 2.4 children per family, whereas elsewhere on the continent it's double that. The key to make it work will be better policy, better education, especially for girls, and better stability which would allow for better management of this problem. Look at Asia, where birth rates have been brought down. Now, if China wants to bring it back up it can afford to do so. The president was at pains to explain during a breakaway session of the Council on Foreign Relations (CFR) that land reform is a domestic issue that will be resolved in the uniquely South African way. Should we be concerned about the way the land issue is framing his presidency and South Africa's standing in the international community?I thought that Ramaphosa did an outstanding job of reminding the world that land reform is a complicated issue. By referring back to Mandela he was very shrewd. He once again reminded everyone that the South African people and their leader surprised the world by getting through the transition from apartheid to democracy peacefully. He then gave a long, detailed answer to the chairperson of the CFR. He said in his own deliberate way, much like that of former US president Barack Obama, that this is an issue that has to be accommodated; there is a history that informs it, and the international community should trust the South African government to make an effort to do it right. Should we be worried by threats that the US might cut its foreign aid to South Africa if we don't adopt a "friendlier" appraoch to the them in future?If Trump does go through with scrapping the AGOA agreement and slapping a 25% tariff on automobile imports to the US, that would have huge consequences for South Africa.However, because Trump's domestic authority is diminishing very quickly, I believe we'll see a curtailment of his powers after the midterm elections in the US in November. Aid to Africa has been one of the few things that's enjoyed bipartisan support in the US Congress for many years. So Trump's threats in this regard will likely be tempered by the political realities. South Africa's minister of trade and industry, Rob Davies, will also have been attentive to the president's intentions regarding AGOA and would have been lobbying in Washington against it. President Trump drew laughter from the UN General Assembly when he said that his administration is the best the world has ever seen. What does this say about how he is viewed by the international community?This is, as he would say, "huge". No American president has been laughed at like that. It captured the lead of the local newspapers because Americans have been dealing with his lying and exaggeration and narcissism for the past two years and here he is, saying these things in front of the elites of the world and they're scratching their heads. It means his fraudulence and misrepresentation of the facts are being exposed on the global stage. But there's also a connection with South Africa. Ramaphosa has a great asset in the legacy of Nelson Mandela. This whole year of celebrating 100 years of Mandela isn't just some castle in the sky. It serves to give Ramaphosa cover. It brought Obama to South Africa for the annual memorial lecture where he did the same thing that Ramaphosa now did at the UN. It really drew the line and showed the contrast between those more generous leaders who are trying to do what they can to make the world a better place and those (read: Trump, Jacob Zuma) who seem to be in it for personal reasons.