Welsh independence must be "on the table" after Brexit, Plaid Cymru's new leader has said.
Adam Price said if there was a "hard" Irish border and the UK left the EU single market and customs union "the appetite for Scottish independence and Irish unity" would be "insatiable".
He warned of a Wales "at the mercy of Westminster".
Comparing Brexit to the Titanic, Mr Price told Plaid's autumn conference in Cardigan that the "iceberg's looming".
The assembly member, who defeated Leanne Wood in the party's recent leadership contest, said voters should be given a chance to "avert a disaster" through a referendum on the final Brexit deal.
But Theresa May's proposals have been attacked by both Brexiteer and pro-EU Tory MPs, while the European Union's chief Brexit negotiator Michel Barnier has said he is "strongly" opposed to key parts of her plan.
Pitching for independence, Mr Price told conference: "We can be fair and flourishing. We can be self-governing and successful. We can be Welsh and European."
In his speech Mr Price accused unionist parties of being devoid of ideas.
"The cupboard is bare," he said, claiming Labour represented "the politics of the past".
The leader promised a "new vision for health and care" that NHS founder Aneruin Bevan "could only dream of", with reviews to examine the creation of a National Care Service and whether GPs should continue to act as private operators.
Mr Price said Plaid in power would build a "National Western Rail Line" from Swansea to Bangor, and promised a "comprehensive child package" so parents could return to work when they choose.
"We must fire up the national imagination with a sense of the Wales that might yet be," he said.
"We cannot afford to keep doing what we have done for another five years."
Plaid's new leader admitted the party had to "transform" and needed an "honest assessment" of itself.
He has commissioned former SNP Westminster leader Angus Robertson to conduct a "root and branch review" of the party's campaign machinery.
By BBC Wales political editor Felicity Evans
Plaid's new leader was greeted by a standing ovation before he uttered a word.
Adam Price's speech was chock full of historical references, including the use of the long bow by the Welsh armies at the battle of Crug Mawr here in Cardigan - the weapon, he noted, of a David confronted with a Goliath.
Today he wants to deploy ballot boxes for two referendums - one on Welsh independence and one on Brexit.
Plaid Cymru members will love this, but it is a risky strategy that could alienate more voters than it attracts.
Wales opted for Brexit in 2016 and the issue remains divisive. On independence - polls suggest the vast majority of people oppose the idea.
But Adam Price wants a message that can cut through the political noise, and his is strategy is this: energise the base, seek credibility with the wider electorate with a clarity about what the party stands for and reform the party's campaign machinery.
Currently, Plaid is the third largest party in the Welsh Assembly so there's a steep road ahead to the next election in 2021.
Before conference began on Friday, Mr Price said Brexit was threatening a "constitutional crisis - with or without a deal", claiming that: "The appetite for Scottish independence and Irish unity will become insatiable."
Welsh independence, Mr Price said, "must be on the table" in order to "ensure that our country isn't swallowed into an 'England and Wales' entity where we are at the mercy of Westminster".
The Plaid Cymru leader said that if his party was in government after the 2021 election in Wales, it would "put a Welsh Independence Referendum Act on the statute book at the earliest possible opportunity".