president obama told the united nations<u+00a0>on monday that they<u+00a0>must all work together on an array of challenges <u+2014><u+00a0>from syria to ukraine, from poverty to climate change <u+2014><u+00a0>because "the united states cannot solve the world's problems alone."









while making a largely thematic address to the u.n. general assembly<u+00a0>about the need for<u+00a0>global cooperation, obama also had harsh words for russia just hours ahead of a tense meeting with president vladimir putin later on monday.









the president criticized russia's aggression in eastern ukraine and its annexation of crimea, saying "we cannot stand by when the sovereignty and territorial integrity of a nation is flagrantly violated."









while not citing<u+00a0>the russian president by name, obama also<u+00a0>challenged putin's assertion that the only solution to the conflict and refugee crisis syria is to back bashar al-assad, describing him as a tyrant "who drops barrel bombs to massacre<u+00a0>innocent children."









throughout his 42-minute speech, obama also defended the iran nuclear agreement<u+00a0>and questioned a chinese<u+00a0>military build-up in the south china sea that has drawn protests from u.s. allies like japan and south korea. he<u+00a0>extolled the new u.s. approach to cuba, and called on congress to lift the decades-long economic embargo against the communist island.









obama also pledged to continue the fight against the threats of the islamic state <u+2014><u+00a0>"we will not be outlasted by extremists" <u+2014><u+00a0>but said other nations need to participate, a common theme of his u.s. address.









"together, we must strengthen our collective capacity to establish security where order has broken down, and to support those who seek a just and lasting peace," obama said.









u.n. members also need to work together to face challenges ranging from extreme poverty to violence against women to trade and global economic development to<u+00a0>the ravages of climate change, obama said.









referring to a<u+00a0>conference in december<u+00a0>seeking a global climate change agreement, obama said "the united states will work with every nation that is willing to do its part so that we can come together in paris to decisively confront this challenge."









in stressing the need for multi-lateral action, obama cited the u.s. problems with the war in iraq, citing "the<u+00a0>hard lesson that even hundreds of thousands of brave, effective troops, trillions of dollars from our treasury, cannot by itself impose stability on a foreign land."









obama also criticized dictatorships and authoritarian governments across the globe,<u+00a0>including iran where hard-liners continue to criticize the united states in spite of the lifting of sanctions in the wake of the nuclear deal. "chanting death to america does not create jobs, or make iran more secure," obama said.









recent history proves that "dictatorships are unstable," obama said: "you can jail your opponents but you can't imprison ideas."









speaking 70 years after the founding of the united nations, obama praised the work of the organization founded in the ashes of world war ii and designed an to prevent a third global conflict.









through its work, obama said, lives have been saved, agreements forged, diseases conquered, and mouths fed, although "we come together today knowing that the march<u+00a0>of human progress never travels in a straight line, that our work is far from complete,<u+00a0>that dangerous currents risk pulling us back into a darker, more disordered world."









later on monday, obama meets separately with two powerful world leaders: prime minister narendra modi of india, and putin of russia.









speaking to the general assembly shortly after obama,<u+00a0>putin<u+00a0>said countries should back assad because his government in syria is<u+00a0>fighting islamic state militants. the russian leader<u+00a0>chided the u.s. for backing syrian rebels, saying some of them have defected to the is.









as for ukraine, putin said a<u+00a0>"coup" that evicted a pro-russian leader has led to a civil war in that country.









obama will also attend<u+00a0>a u.n. luncheon, chair<u+00a0>a meeting on peacekeeping efforts, and host<u+00a0>a reception for general assembly delegates.









as obama spoke to delegates at the united nations, the white house issued a memorandum pledging support for peacekeeping missions, and ordering executive agencies to help. the united states<u+00a0>is looking for similar pledges from other nations, and obama told u.n. delegates<u+00a0>that "we have to do it together."









during<u+00a0>his speech to the general assembly, obama also made references of some of politics surrounding the u.s. presidential election. in an apparent reference to republican presidential candidate donald trump, obama denounced voices who call for "walls" designed to "keep out immigrants."









in his repeated call for<u+00a0>greater global cooperation, obama noted what he called "increasing skepticism of our international order," and of government in general. he blamed some of it on "greater polarization, more frequent gridlock," and various movements "on the far right, and,<u+00a0>sometimes, the left."









critics of the system are also exploiting "the fears of ordinary people," obama said, creating "a<u+00a0>politics of us versus them."









globalization is fact, however, and "we cannot look backwards," obama said.









"we live in an integrated world," he said, "one in which we all have a stake in each other's success."
obama: u.s. cannot solve the world's problems alone
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