If any one factor were decisive, it would be the role that the EU was to play in providing the stick-and-carrot combination that is the Birds Directive.
I've been visiting Europe's most important conservation areas for over 30 years, as an adviser and campaigner, and as a naturalist. And none is more special, or more emblematic of conservation struggles, than the Coto Doñana in southern Spain.
I first gazed over its vast marshes, explored its forests, and revelled in its unique culture in 1988, and have been back for business or pleasure at least thirty times since.
Back in the late 1980s, there was a real sense of industry's Goliath trampling on the fledgling conservation movement's David. Huge mass tourism projects were being planned that would have needed so much water from Doñana's aquifers they would have sucked the marshes dry.
The decisive factor - the Birds Directive
A good old-fashioned fight between claims of massive job opportunities and claims of impending doom ensued. Add in some good old-fashioned allegations of corruption and the media began to take interest. Conservation was making an impact on the public consciousness.
Wind forward a couple of years: David won and Goliath lost. There was no single sling-shot, rather a gathering together of evidence, law and protest, and growing national pride in the places that make Spain special.
But if any one factor were decisive, it would be the role that the EU was to play in providing the stick-and-carrot combination that is the Birds Directive.
This conservation law sets the standards that all Member States need to meet, and forms the basis for cooperation in managing the continent's shared heritage.
Realising the economic potential of nature
I was a member of a Brussels-based panel working on Europe's threatened wetlands, under the auspices of the European Commission. These great places had the legal protection - at EU level at least - they needed.
But the complex demands of different sectors, and the lack of coordination between them, meant that drainage or abstraction for agriculture, inappropriate river management, tourism and any other ill you can name, were threatening them all.
This was not helped by the same lack of coherence between EU policies causing some branches of the Commission to fund the very destruction that others were trying to prevent.
We soon saw Doñana as the leading example of what may go wrong and what was at stake. So as well as using the stick - the threat of a European Court judgement against Spain - we were keen to see investment directed at enhancing nature, and realising its economic potential.
The carrot was EU money, €225 million, invested over ten years in conservation, coordinated management, and alternative development propositions. It was one of the first and biggest investments of EU development funds in the green economy.
Disaster strikes - a toxic tide of mine waste
In the last two months, I have been back to Doñana twice, with journalists from the BBC's Costing the Earth and The Observer, my first working visits for over ten years.
We were following up another story of near-disaster that unfolded in 1998. That was a new kind of environmental tragedy, involving a reservoir of toxic sludge, whose dam collapsed in the hills above Doñana, releasing a 5 million tonne tsunami of mining residue into the rivers below.
Some 5,000 hectares of farmland were rendered useless for ever, and heavy metals started to be taken up by plants, and then birds, with several years of discernible impact on breeding success and mortality. A commercial shell fishery was closed, affecting hundreds of families.
By this time, SEO/BirdLife and WWF Spain had come of age and were leading the charge, the local and national governments responded with tremendous resolve and the headlines ran for weeks.
An opportunity make it better than before
Things had changed in Spain. As a UK conservationist I was hugely impressed. This was not a fight against something, it was a fight for something, with everyone on the same side.
Over the following months, I watched as trucks from Hungary, France, Romania were pressed into the task of clearing the surface layer of sun-baked toxic mud. Intellectual resources were also pooled.
Far from being shut out of discussions, SEO/BirdLife, RSPB and our partners were at the table, our ideas and expertise actively sought. We started to imagine a Doñana that could be even better than before the accident.
Most impressive of all was the long-term vision that emerged from disaster. 'Doñana 2005' was a restoration programme the like of which I had never seen.
It was not merely about cleaning up and putting things back together again. It was about solving some chronic problems, even restoring some of the ecological functioning that had first been lost back in the 1950s, when the United Nations helped Spain transform 1 million hectares of wetland into farmland.
As I met up with former colleagues, I saw that Doñana 2005 is behind schedule. But it is very much alive, with no let-up in ambition and many of the works complete.
The most ambitious project, to reconnect a lost branch of the Guadalquivir river with the marshes, is on track for 2014, returning three thousand hectares of reclaimed land to nature.
EU Directives provide the framework for protection and investment
Hundreds of millions of euros have been invested in Doñana's future by NGOs, government, and, in particular, the EU, which funded most of Doñana 2005's €130 million price tag.
It is the Birds and Habitats Directives that define which places need this protection and have the opportunity for investment.
So do the Directives guarantee an area's future? Not necessarily. In the Coto Doñana, conservation groups are fearful of proposals to reopen the failed mine, albeit with new technologies aimed at preventing the build-up of sludge.
Illegal and legal water abstraction continues. There is talk of a gas pipeline, and there will always be something around the corner to fear.
Do we need an extra layer of European law?
In the UK, our conservation legislation has a long pedigree, the main features of it pre-dating the Directives by decades. We have come to see it either as a tool to support protection or a blockage on development. Why add another layer from Europe?
This is to miss the fact that even here, working to agreed European standards has unlocked hundreds of millions of pounds to encourage farmers to play their part, and hundreds of millions more for local authorities, charities and businesses in the green economy.
EU Directives aren't all-powerful, but at least they provide a secure legal basis for NGOs and governments to keep working to safeguard places like Doñana, and many others closer to home, for Europe's future generations.
Laurence Rose ran the RSPB's European Department between 1988 and 2000, was Regional Director for Northern England and is now Senior Sites Manager for the RSPB in Norfolk.
Follow Laurence Rose on Twitter: @Laurence_R_RSPB.