Below is a percentage comparison chart of the Dow 30, S&P 500, Nasdaq 100, and Russell 2000 Indices, and the Financials ETF (XLF). I've started it from the October 2011 lows.
As you can see, the Russell 2000 Index has been leading the advance from that point on a percentage-gained basis until the second-place XLF shot above it on March 13th.
The Russell 2000 has been, effectively, in a basing mode since February, but has been moving up from its low of last week and is now near the highs of this year. It had begun pulling further and further ahead of the other Major Indices from mid-December, and they have closed the gap to the point now where they have all been moving up "in tandem" from last week's lows.