Garvan Walshe is a former National and International Security Policy Adviser to the Conservative  Party.  He runs Brexit Analytics 

Today is the 100th anniversary of the Balfour Declaration, in which Britain promised to facilitate the establishment of a “Jewish National Home” in Palestine, territory it had taken over from the declining Ottoman empire and where, since the end of the previous century, the Zionist movement had begun to organise a community of Jewish immigrants as part of its plan to create a nation state for the Jewish people.

Also today, Carles Puigdemont, Catalonia’s answer to David Ben Gurion (Anna Gabriel is most clearly the homologue of Ze’ev Zhabotinsky) finds himself in Brussels, a fugitive from Spanish justice under a charge of “Rebellion” having arranged for the Catalan parliament to declare unilateral independence.

Both movements appeal to the principle of the self-determination of peoples: the idea that a people should govern itself, and not be under the control of an entity it considers foreign. On its face it sounds eminently reasonable, but immediately raises just the thorny political questions it is supposed to solve.

The most obvious is what is to count as “a people”? Trying to define a nation is a fool’s errand (Golda Meir’s rhetorical “Who are the Palestinians? I am a Palestinian!” didn’t age well).

Language isn’t the help it appears to be. The Irish speak English. Many Ukrainians speak both Ukrainian and Russian. It doesn’t mean they want to be ruled from Moscow. A very large proportion of Catalans don’t, in fact, use Catalan on a daily basis, and the major Spanish language publishers are, it turns out based in Barcelona, not Madrid.

Then there’s the apparently small matter of where the state should be located. Only the Zionist movement faced this choice directly. The Third Zionist Congress debated establishing the Jewish state in Africa instead of the Middle East. Palestinians, trying to be clever, sometimes propose it. But we can be sure that Tanzanians and Ugandans would have been every bit as opposed to Zionist pioneers moving into their territory. It would not have served the Jews well to have fled the Tsar and Hitler to end up at the mercy of Idi Amin.

But Catalans face this question indirectly. Barcelona is strongly against independence. Yet a Catalonia independent against the wishes of its historic capital would breed endless tension, while one that excluded it would be absurd (and prone to irredentist attempts to recover the city).

Peoples, unfortunately, are not neatly organised around the territories their national movements want to claim. Others – the Spanish, the Palestinians – have equal and opposite rights to self-determination, recreating the problems in mirror image. Sometimes compromise is possible – autonomy, partition, or even power sharing – but not always. It is hardly unknown for reasonable compromises to be rejected for political reasons.

Worse, one side’s victory, with mathematical inevitability, generates a defeat on the other side to be avenged. Far from resolving a conflict over territory, a claim to self-determination is much more likely to start one.

But – and it is an important but – this doesn’t make self-determination wrong. It isn’t always right or reasonable to avoid a conflict: the Jews, in particular had to fight for statehood against enemies determined to finish the job the Nazis started. The Arabs of the Palestine of the British Mandate (it would be the Zionists’ efforts to create the State of Israel that would forge their identity as specifically “Palestinians”) resented the immigration of Jews who wanted radically to change the character of where they lived and resisted it violently.

The Catalan movement is far less bloody. But its more extreme elements oppose the migration of “foreign” Spaniards, who don’t want independence. If the fate of territory depends on the composition of its population, it assumes the highest political importance.

The tragedy of self-determination is not that it is too hard to achieve but that it’s too easy to assert. A group that claims it doesn’t end a conflict. It begins one.

The relevant question is whether that conflict is justified. Hearing of the ceremonial defrocking of Alfred Dreyfus, the French Jewish soldier framed as an Austrian spy, Theodor Herzl concluded that Jews couldn’t trust their protection to assimilating within European society. The decades that followed proved his fears right. As Hannah Arendt wrote in her account of Eichmann’s trial, when they want to persecute you, they first make you stateless.

But Catalans don’t face persecution (let alone the Holocaust). Their language is taught in schools. Their version of history lavishly subsidised by the regional government. Their argument with Madrid is over the amount of autonomy and public spending, and the number of red and yellow stripes on the flag.

The Balfour Declaration was one of the kinder acts of British imperialism. Without it there would have been no Israel and nowhere for the survivors of the Holocaust, or the Jews of North Africa and Iraq, Iran and Yemen, to escape to.

Zionism is self-determination of necessity. The conflict of which the Balfour Declaration was a part could not be avoided. But the Catalan nationalist effort is self-determination of choice, creating new wounds without reason.