If we were one whole planet and not several countries?

Why can't everyone start acting like one whole planet instead of just a bunch of countries. In this way we could solve our problems as a planet, and resources would be distributed equally. There would be less of country patriotism, bad rulers, and war. Why can't people stop acting like squabbling little immature kindergartners and instead act like the grown-ups they are?! Separate countries all with different systems of government are just going to destroy the planet and themselves. We need to be one united planet, not individual countries! What is your opinion of this?