„So the whole war is because we can't talk to each other.“

„Men are at war with each other because each man is at war with himself.“

—  George S. Patton United States Army general 1885 - 1945

This is almost always attributed to US Ambassador Francis Meehan http://www.nndb.com/people/060/000121694/, though without citations, and only very rarely to Patton.
Misattributed

„On the contrary, it's because somebody knows something about it that we can't talk about physics. It's the things that nobody knows anything about that we can discuss. We can talk about the weather; we can talk about social problems; we can talk about psychology; we can talk about international finance — gold transfers we can't talk about, because those are understood — so it's the subject that nobody knows anything about that we can all talk about!“

—  Richard Feynman American theoretical physicist 1918 - 1988

Rejoinder when told that he couldn't talk about physics, because "nobody [at this table] knows anything about it."
Part 5: "The World of One Physicist", "Alfred Nobel's Other Mistake", p. 310.
Quoted in Handbook of Economic Growth (2005) by Philippe Aghion and Steven N. Durlauf.
Surely You're Joking, Mr. Feynman! (1985)

„We're all one thing, like cells in a body. 'Cept we can't see the body. The way fish can't see the ocean. And so we envy each other. Hurt each other. Hate each other. How silly is that? A heart cell hating a lung cell.“

—  Charlie Kaufman American screenwriter 1958

Origine: Adaptation.: The Shooting Script

„I'm mad about the waste that happens when people who love each other can't even bring themselves to talk.“

—  Alice Walker, libro The Temple of My Familiar

Origine: The Temple of My Familiar

„The Conservatives can't talk of class war: they started it.“

—  Stanley Baldwin Former Prime Minister of the United Kingdom 1867 - 1947

G. M. Young, Stanley Baldwin (1952), p. 31
Undated

„I was trying to say that, really, a man and a woman, can't understand each other because we are a man and a woman. And if we could actually swap each other's roles, if we could actually be in each other's place for a while, I think we'd both be very surprised! … And I think it would lead to a greater understanding.“

—  Kate Bush British recording artist; singer, songwriter, musician and record producer 1958

On her song "Running Up That Hill (A Deal with God)", in a Radio 1 Classic Albums interview with Richard Skinner (26 January 1992) http://gaffa.org/cloud/music/running_up_that_hill.html
Contesto: I was trying to say that, really, a man and a woman, can't understand each other because we are a man and a woman. And if we could actually swap each other's roles, if we could actually be in each other's place for a while, I think we'd both be very surprised! … And I think it would lead to a greater understanding. And really the only way I could think it could be done was either... you know, I thought a deal with the devil, you know. And I thought, "well, no, why not a deal with God!" You know, because in a way it's so much more powerful the whole idea of asking God to make a deal with you. You see, for me it is still called "Deal With God", that was its title. But we were told that if we kept this title that it would not be played in any of the religious countries, Italy wouldn't play it, France wouldn't play it, and Australia wouldn't play it! Ireland wouldn't play it, and that generally we might get it blacked purely because it had God in the title.

„When we talked, I talked about me, you talked about you, when we should have talked about each other.“

—  Jean-Luc Godard French-Swiss film director, screenwriter and film critic 1930

„Standing next to Micah, I realized that there were times when we talked not because we needed to communicate anything important, but simply because we each drew comfort from the other's voice.“

—  Nicholas Sparks American writer and novelist 1965

Nicholas Sparks, Chapter 9, p. 138
2000s, Three Weeks with My Brother (2004)

„I have talked with Betsy, and Betsy has talked with me,
And so we've agreed together that we can't never agree.“

—  Will Carleton poet. 1845 - 1912

Betsy and I Are Out (1871)

„Lonely people, in talking to each other can make each other lonelier.“

—  Lillian Hellman, The Autumn Garden

The Autumn Garden (1951)

„That’s love: Two lonely persons keep each other safe and touch each other and talk to each other.“

—  Rainer Maria Rilke Austrian poet and writer 1875 - 1926

„Men often hate each other because they fear each other; they fear each other because they don't know each other; they don't know each other because they can not communicate; they can not communicate because they are separated.“

—  Martin Luther King, Jr. American clergyman, activist, and leader in the American Civil Rights Movement 1929 - 1968

In reference to the Alabama Council on Human Relations, an organization which was joined by King, whose church's meeting room was used to hold monthly meetings for the Montgomery chapter the council. Stride Toward Freedom: The Montgomery Story (1958)
1950s
Contesto: Although the Montgomery council never had a large membership, it played an important role. As the only truly interracial group in Montgomery, it served to keep the desperately needed channels of communication open between the races.
Men often hate each other because they fear each other; they fear each other because they don't know each other; they don't know each other because they can not communicate; they can not communicate because they are separated. In providing an avenue of communication, the council was fulfilling a necessary condition for better race relations in the South.

„Men in plural […] can experience meaningfulness only because they can talk with and make sense to each other and themselves.“

—  Hannah Arendt, libro Vita activa

Origine: The Human Condition

„Lovers never get tired of each other, because they are always talking about themselves.“

—  François de La Rochefoucauld, libro Reflections; or Sentences and Moral Maxims

Ce qui fait que les amants et les maîtresses ne s'ennuient point d'être ensemble, c'est qu'ils parlent toujours d'eux-mêmes.
Variant translation: What makes lovers and their mistresses never weary of being together is that they are always talking about themselves.
Maxim 312.
Reflections; or Sentences and Moral Maxims (1665–1678)

„I've always believed that a lot of the trouble in the world would disappear if we were talking to each other instead of about each other.“

—  Ronald Reagan American politician, 40th president of the United States (in office from 1981 to 1989) 1911 - 2004

„We knew each other. We talked. We passed each other going to the set of our own films. We were doing our jobs. We had great mutual respect.“

—  Greta Garbo Swedish-American actress 1905 - 1990

Lillian Gish

„You needn't be so scared. Love doesn't end. Just because we don't see each other…“

—  Graham Greene, libro The End of the Affair

Origine: The End of the Affair

„I can't give you answers on what we know and don't know, other than what's charged in the indictment. It's not because I enjoy being in that position. It's because the law is that way. I actually think the law should be that way. We can't talk about information not contained in the four corners of the indictment.“

—  Patrick Fitzgerald American lawyer 1960

Fitzgerald News Conference from nytimes.com (October 28, 2005) http://www.nytimes.com/2005/10/28/politics/28text-fitz.html?pagewanted=all

„We love each other like matches in the dark. We don't talk, we catch fire instead“

—  Mathias Malzieu, libro La meccanica del cuore

Origine: La Mécanique du cœur