An economic conference in Beijing last week opened with a distinctly political statement: the most important diplomatic relationship on earth - for now and the near future - is that between the United States and China. How it fares, the organiser said, would decide much about global stability in general, not only about the regional trade and investment issues so important to the conference itself.
But just now this relationship is not doing well and, by the end of the week, it could become much worse. For decisions are due today about US arms sales to Taiwan, the explosive issue that periodically threatens to sabotage broader ties between China and America.
This time the issue involves new elements. After some relatively quiet years, Taiwan seeks major weapons upgrades. It calls them crucial for self-defence now that China is adding modern Russian aircraft and deploying offensive missiles within easy range of Taiwan's main cities. But Beijing warns its relationship with Washington will suffer greatly if the most modern arms are supplied and says it retains the right to seize Taiwan by force if persuasion fails.
The basic issue dates from American support in the 1950s of nationalists in Taiwan as an alternative to communists in the mainland. Although that approach was dropped long ago, all US administrations are required by law to supply Taiwan with enough weapons to ensure that political unification does not result from military means.
At the same time, the US has stated that it 'does not seek to carry out a long-term policy of arms sales to Taiwan', and will not exceed 'in either quantitative or qualitative terms' certain levels of supply. Over time, Washington is also committed to 'reduce gradually' these sales.
Needless to say, these conflicting guidelines bring recurring problems. During their friendliest years, Washington, Beijing and Taipei manage to apply them with great ambiguity and restraint. This time, however, some clearer lines are being drawn and grave disputes seem all too possible.