Prime Minister Shinzo Abe took office determined to transform Japan's role in the world. That goal topped the agenda of his four-nation tour of Europe last week. Mr. Abe is ambitious but he must be cautious when considering Japanese participation in multilateral security operations.

The new thinking underlying Mr. Abe's trip was signaled on the day of his departure with the elevation of the Japan Defense Agency to become the Ministry of Defense. That move sets the stage for a shift in defense planning as Japan attempts to take on new international responsibilities. Central to that new role is permanent membership on the U.N. Security Council: Mr. Abe made that case in meetings with British Prime Minister Tony Blair, German Chancellor Angela Merkel, French President Jacques Chirac and European Commission President Jose Manuel Barroso, and won support from them all. Of course, much remains to be done before that goal can be realized -- meaningful U.N. reform encompasses much more than just expanding the size of the Security Council. Mr. Abe focused his efforts on building a coalition that supports Japanese ambitions.

Three other issues figured prominently in Mr. Abe's discussions in Europe. The first was China's military buildup and the challenges that it poses for regional security. He called for greater transparency by Beijing and asked European governments to maintain the moratorium on arms sales to China that was imposed in the aftermath of the 1989 Tiananmen killings. Two years ago, European leaders appeared ready to lift the embargo and take a share of the rapidly expanding Chinese arms budget. Strong U.S. objections and Beijing's Anti-Secession Law dampened European enthusiasm but some leaders still see arms sales as a way of building a stronger relationship with China. Mr. Blair and Ms. Merkel backed Mr. Abe's request; Mr. Chirac hedged.