The election of five MPs from the anti-capitalist Podemos ("We Can") in Spain has rocked the political establishment.
Formed only four months ago, Podemos won a staggering 1.2 million votes - mostly from young people who do not usually vote, but also from many working class voters disillusioned with the social democratic PSOE. With the Communist Party led United Left (IU) tripling its vote since the last EU elections, the left took over 20 percent of the vote.
In contrast, the combined support for the two main parties, the ruling conservative Partido Popular (PP), and the PSOE, plummeted to under 50 percent - compared to the 80 percent they had regularly received since the 1970s.
To make matters worse for the PP, left nationalists won both in the Basque Country and in Catalonia - showing the depth of support for independence.
The cracks that appeared are now threatening to become seismic, with the resignation of the PSOE leader and then on 2 June the abdication of the king.
Podemos has its roots in the indignados 15M movement which occupied hundreds of squares in May 2011 protesting against the political set-up and austerity.
During 2012, 15M dovetailed into the growing resistance to cuts - its activists were central to the rank and file movements (the mareas or "tides") launched to defend education, health and public services and in two general strikes that year.
15M activists have also been central in the Anti Evictions Campaign (PAH), which has prevented hundreds of families, indebted to the banks, from being evicted.
But life remains dire for many people. Around 22 percent of the population living under the official poverty line; some 30 percent of children are at risk of falling into poverty. Unemployment stands at 26 percent and over 54 percent for those under 25.
Resistance, although more fragmented, has continued over the past year, including strikes against redundancies. In particular, the Marches for Dignity, called by several small left unions, culminated in a million-strong demo in Madrid.
It was against this background that activists launched Podemos with a programme based on many of the demands that came out of the squares - such as ending austerity, cancelling the debt and bringing financial institutions under democratic control. It has also defended abortion rights and the right to self- determination for the national minorities.
Podemos's structure mirrors that of the indignados - based on open assemblies. The 64 candidates for the Euro-elections were chosen through an on-line primary in which over 33,000 people voted. Those involved are overwhelmingly non-aligned activists. Organised revolutionary socialists also have a small presence.
Central to its success has also been the role of its figurehead, Pablo Iglesias. The 35 year old university lecturer is popular due to his prominence on TV chat shows denouncing corruption and neoliberalism.
Inevitably a project like Podemos, with no clear structure and a very general programme, has many potential problems. Insistence on an open assembly-based structure has marked
Podemos apart from IU. Despite insisting on the need for unity, it is unlikely that United Left in local government would break alliances with the PSOE.