I don't believe most of the answers are actually tackling the question; which appears to be: how can you make people see each other as people, not just pretend they respect them. Furthermore, specifically, are these three ideas about that realistic?
A popular response so far has been just throw a common enemy in the mix. In war you pretend that you and your ally get along, while really you plot how to dispose of them after you've dealt with the common threat. But this doesn't explain most of human history. From the fall of the Ottoman empire many in the Arab world had a vision of a future where the Arab nations would unite, and form their own USA. Even though they had a common enemy (Israel/America) this never happened, because in the end the common enemy did not make them see each other differently.
Indeed we have many more examples like this from history. During the Spanish Civil War the communists backed by the USSR turned on their anarchist comrades mid-fight, and started murdering them instead of the nationalist enemy. And the allies during the Second World War didn't become best friends forever as a result of their common Nazi enemy. In fact even before the war was over Chuchill was drawing up plans for Operation Unthinkable, to paradrop soldiers into Moscow and kill Stalin in order to win the next war before the last was even over.
There's an even more interesting contrary example, where war made absolutely no difference to who your friends were. During the Persian invasion of Greece, Persia's relatively small ethnic Persian army was supplemented by a large number of mercenaries from all over the place, and the Persian nobility actually preferred Greek bodyguards, even during the war. After the invasion failed they figured they'd not push the issue... but then were so impressed they asked if they could hire Greek soldiers, and they did. Much like how Britain's failure to conquer Nepal led to the creation of the Royal Gurkha Rifles, and Britain guaranteeing Nepal's independence. So it seems more likely that actually, you'll become friends with your enemy than ally. Reality is stranger than fiction!
There are however ways to make people see each other in more favourable terms. It is false to say humans can't see each other more sympathetically because of biology. In that case we'd all still be living in primitive and small tribes.
But we've got better at seeing foreigners as human in recent times, after something of an embarassment of the last few centuries. Trade is an important factor in this explosion of empathy and tolerance. We've become richer, and thus more able to travel and explore, and the more people we meet the more we realise they're just like us, and the greater globalisation, the more we depend on and value the skills and contributions of those different to us.
Consider America. The revolutionary war wasn't because the colonists hated Britain, but because they really wanted to try something new. And in the early days the only real Americans of course were white protestant males. Now almost all white protestants view white Catholics as quintessentially Americans too, that isn't a thought which crosses most people's minds; that back then catholics weren't considered proper. And now many other groups are also thought of by most people as being fully American, collective empathy has increased as immigration, integration, trade, wealth, and education have increased.
Many ideas have been created to attempt to unite people. Kings united tribes under feudalism, and Nations united kingdoms under Nationalism. Missionary religions tend to be inclusive as they're always seeking new members. Christianity, Islam, and Buddhism don't care much for anything besides the loyalty of their congregation. If you're in the club, they love you. They are united by their love of something... much like death metal fans.
Indeed we have examples where people have had this experience, one of the most noteworthy being Malcolm X's revelations during his Hajj in Mecca. Beforehand he had spent most of his time with the Nation of Islam, which was a racist and odd sect of Islam unique to America's black community. He had believed that whites and blacks couldn't get along, and that whites were all evil. But then:
During the past eleven days here in the Muslim world, I have eaten
from the same plate, drunk from the same glass, and slept in the same
bed (or on the same rug) -- while praying to the same God -- with
fellow Muslims, whose eyes were the bluest of blue, whose hair was the
blondest of blond, and whose skin was the whitest of white. And in the
words and in the actions and in the deeds of the "white" Muslims, I
felt the same sincerity that I felt among the black African Muslims of
Nigeria, Sudan, and Ghana. We were truly all the same (brothers) --
because their belief in one God had removed the "white" from their
minds, the 'white' from their behavior, and the 'white' from their
attitude. I could see from this, that perhaps if white Americans could
accept the Oneness of God, then perhaps, too, they could accept in
reality the Oneness of Man -- and cease to measure, and hinder, and
harm others in terms of their "differences" in color.
Other ideologies, like anarchism, socialism and communism, also sought to unite the people of the world and for them to think of each other as comrades. It should then be little surprise that it was not long after the fall of communism in Yugoslavia, that ultra nationalists emerged and began butchering each other - they no longer had reason to believe what they had been told, that people were fundamentally equal.
Of course, the factors which can be used to unite people can also be used to divide people. But that's true of every tool, people can use it for good and evil.
IN CONCLUSION: Common enemies don't often help with empathy, trade often does through exposure, and people aren't inalienably bigoted because humanity has got a lot more interconnected and empathic in recent decades. And yes, when people have babies with their former enemies it kind of makes them start to have empathy too. Incidentally that's the oldest alliance making strategy: I'll let your son marry my daughter if my son can marry your daughter, and then I'll stop stealing your cows and plotting to murder you. The best strategy for promoting empathy is encouraging education, trade, and interaction. Bedroom diplomacy isn't a bad idea either.