So, with the heaving sound of an old tree suddenly splitting apart in a storm, the labor movement is finally breaking up.

On Sunday, leaders of four of the country’s largest labor unions announced they would boycott this week’s AFL-CIO convention, and officials from two of those unions, SEIU and the Teamsters, withdrew from the Federation on Monday.

The five unions now comprising the Change To Win Coalition (CTWC)–along with SEIU, the Teamsters, United Food and Commercial Workers, Laborers, and UNITE HERE–have formed what amounts to a rival federation–whether they all formally leave the AFL-CIO or not, which now seems likely. These unions’ collective 5 million membership represents 40 percent of the AFL-CIO’s 13 million total. If the mammoth 2.7 million member National Education Association aligns with the effort, CTWC will hold exactly half of all union members in the United States.

The break is the biggest rift in labor since the 1930s, when the CIO split off from the AFL.

The avowed basis of the break is a fundamental disagreement on strategy, often depicted as a choice by the insurgents of organizing over politics. This is misleading. Many of the unions remaining in the federation are every bit as committed as the CTWC group to organizing new union members. And some CTWC unions, particularly SEIU, are keenly aware of the importance of politics in increasing union membership. The fight is really about consolidation and political focus.

SEIU has argued that the current practice of having several unions competing in single industrial sectors–“15 separate organizations in transportation, 15 in construction, 13 in public employment, nine in manufacturing, and so on”–defeats the scaled effort needed to take on business in today’s climate. It wants to compel fewer, bigger, more clearly sectorally-based unions, as in northern Europe. And it has argued that labor must find ways to mobilize support outside itself, chiefly through more engagement in state and local politics.

It is hard to argue with any of these claims, though whether CTWC can realize its promise is an open question. Even unions without competition in their declared industries are showing declines in density, as indeed are the new Coalition’s own members. And outside SEIU itself, and UNITE HERE in a few cities, few of CTWC’s members show much commitment to the community links and coalition work needed to gain greater influence over state and local politics. In all the shifting of positions over the past seven months, as this “coalition of the willing” has been constructed, the present result sometimes seems less the principled conclusion to a principled debate than the final triumph of testosterone over inertia. The latter is largely produced by the fragmented governing structure of the AFL-CIO, which makes it very difficult to undertake bold initiatives.

But so be it. Labor is now split more or less in half. We can look forward to a long and ugly period of dissension in America’s most important single progressive movement, facing a ruthless anti-worker Administration intent on its complete destruction.

I don’t think this split was necessary, and still think it would have been best for the state of progressive politics if both sides could have worked out a deal on federation reform and leadership transition. (Why didn’t the insurgents run a candidate to contest John Sweeney? Why didn’t they try to move an agenda from within?)

But I also recognize that in the areas of greatest need for labor–organizing, and political engagement and programs in the states and cities–more effective work needs to be done.

So, while I believe that solidarity in the face of an onslaught is preferable, I respect those who argue that standing together may not make sense if they aren’t standing in the right place. And I appreciate the difficulty of changing a troubled organization from within. So I wish the insurgents luck. This country desperately needs a labor movement that is again “the collection of many that speaks for all,” that can provide an organized and intelligent moral center to a majoritarian progressive politics–the folks who brought you the weekend, the eight-hour day, and so much else that makes this country (almost) civilized. I just wish we weren’t starting this way in reclaiming that.