The changing relationship between the Irish and Welsh since the 19th Century is the subject of new research.
Dr Claire Connolly said immigrants in the 1840s were not welcomed
The project aims to explore the countries' political, creative, and cultural ties, starting from the time of the Great Famine in the 1840s.
Researchers from Cardiff and Aberystwyth Universities are involved in the project.
Dr Claire Connolly from Cardiff University, said: "We have ended up talking about being Celtic soul mates".
Dr Connolly, heading the research, said the Irish were unwelcome at first.
She said Irish immigrants escaping the famine were "often strike-breakers, they were hungry, they were desperate, they were looking for work and they didn't understand organised labour or unions".
"They often, in south Wales, undercut local prices and there were around 20 riots in the 19th Century in Wales protesting against the Irish for poor labour practices," she added.
At the time, Wales was at the heart of the industrial revolution, said Dr Connelly, while Ireland was wracked by famine and considered a backward nation.
About a million people in Ireland were estimated to have died of starvation and epidemic disease between 1846 and 1851, and some two million emigrated between 1845-1855.
Dr Connelly, who helped secure funding for the Ireland-Wales Research Network project is hoping to see how and why the relationships between the two countries developed.
Millions of people emigrated from Ireland between 1845-1855
She said: "How, suddenly, in the 20th century can we all be putting our arms around each other in rugby matches and talking about Celtic connections and Celtic cousinships?"
The network, in partnership with Aberystwyth University, aims to develop a deeper awareness of the overlapping histories of Wales and Ireland as well as a fuller understanding of the histories of Britain and Ireland.
Funded by The Arts and Humanities Research Council the network will be launched at a reception at the Consulate General of Ireland in Wales on Thursday.
Colm McGrady, Consul General of Ireland in Wales, said: "This is a very timely and important initiative.
"Wales and Ireland share much in terms of our cultural heritage. The network will undoubtedly contribute to a wider and deeper understanding of the rich tapestry of these links."
The network will also host a variety of public events, starting on 14 December with a reading by Pulitzer-prize winning Northern Irish poet, Paul Muldoon at Cardiff University.