Agreement on immediate ISSUES over a wide swath of the left IS relatively easy, but that's only good enough for coalitions, not a real party. Even a loosely organized one.
I can give personal examples. The group I belong to (Worker's Power-US) is a member section of the League for a Fifth International. This international group thinks we need another Marxist international because the Third was dissolved by Stalin as an accommodation to the western capitalist powers and Trotsky's Fourth International never really got off the ground and sank into irrelevancy. Ergo the need for a Fifth. This is a form of wider left organization internationally, so it kind of fits the bill. Except you have a LOT of Trotskyist groups that don't want to give up any autonomy at ALL, even though the national sections have the major say on national issues. Even though this autonomy is there, the Fourth International groupings don't see the need for a new international and don't want to give up ANY autonomy or the leadership positions they hold in the Fourth. In addition, the OTHER Marxist groups that are not Trotskyists, including the Stalinist Communist Parties worldwide don't seem to think we even need any sort of international organization at all. And even if they DID come around to the idea of an international, say a reconvening of the Third, it wouldn't be with Trots.
But the League is Marxist. What about the Left that ISN'T Marxist? Well there are a lot of anti-capitalists out there who aren't Marxists, mostly of the anarchist stripe. So you could conceivably have an anti-capitalist grouping that would have a lot in common. Or at least the MAJOR commonality of seeing the need for a change in economic system. And there's some movement in THAT direction in Europe with the anti-capitalist parties and united fronts happening all over like Left Unity in Britain and Der Linke, the NAO and others groups in Germany and Austria. This would probably be the actual way to go as it seems to having at least a little success.
But the anti-capitalist left is still a relatively small part of the left. To bring in a wider attendance you'd have to appeal to left reformists who think that capitalism can be "saved" or reformed. Revolutionaries and reformists will never come together even in a loosely organized actual party. Because one group thinks capitalism can be "saved" and one doesn't. Hence, the best that will happen over a broader left is temporary coalitions over specific issues.
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